Atomic Structure And The Periodic Table Flashcards
1
Q
Describe the reactivity of group 7 elements as you go down the group.
A
Decreases
2
Q
Which statement best describes the arrangement of electrons in the plum pudding model?
A
Electrons are randomly arranged throughout the ball of positive charge
3
Q
Which scientist discovered the neutron?
A
James Chadwick
4
Q
Who discovered the plum pudding model?
A
JJ Thompson
5
Q
What physical property is used to separate a mixture of two liquids during distillation?
A
Boiling point
6
Q
Filtration is used to…
A
Separate an insoluble substance from a solution
7
Q
As you go down group 1, the reactivity…
A
Increases
8
Q
What gas is produce when an alkali metal reacts with the water?
A
Hydrogen
9
Q
What name is given to group one elements?
A
Alkali Metals
10
Q
What are the columns called on the periodic table?
A
Groups
11
Q
How many electrons are there in a magnesium atom?
A
12
12
Q
What is an element?
A
A substance that contains only one type of atom.
13
Q
Lithium has an atomic mass of 7 and an atomic number of 3. How many neutrons are there in lithium?
A
4
14
Q
Lithium has an atomic mass of 7 and an atomic number of 3. How many electrons are there in lithium?
A
3
15
Q
Lithium has an atomic mass of 7 and an atomic number of 3. How many protons are there in lithium?
A
3
16
Q
When a liquid evaporates, what happens to the movement of the particles?
A
They move faster
17
Q
Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?
A
• To allow the findings to be independently checked
• This is known as peer review
18
Q
What is irradiation?
A
• The process of exposing a material to nuclear radiation
• The material does not become radioactive
19
Q
What is radioactive contamination?
A
The presence of unwanted radioactive nuclei on other materials.
20
Q
Define the half-life of a radioactive isotope.
A
• The time it takes for the number of unstable nuclei in a substance to halve
• The time it takes for the count rate from a sample to fall to half its initial level
21
Q
Describe the nature of radioactive decay.
A
• Random
• Which nuclei decays and when e is determined only by chance
• It is impossible to predict which nuclei will decay and when
22
Q
State any changes to mass or charge that occur due to the emission of a gamma ray.
A
Both mass and charge remain unchanged.
23
Q
Which type of radiation is least ionising?
A
Gamma radiation.
24
Q
Which type of radiation is most ionising?
A
Alpha radiation
25
What will stop gamma radiation from passing through a point?
• Several centimetres of lead
• A few metres of concrete
26
What will stop beta radiation from passing through a point?
• A thin sheet of aluminium
• Several metres of air
27
What is the range of an alpha particle through air?
A few centimetres (normally in the range of 2-10cm).
28
State four types of nuclear radiation.
1. Alpha particles
2. Beta particles
3. Gamma rays
4. Neutrons
29
Give an example of a detector that may be used to measure count-rate.
Geiger-Muller tube
30
What is count-rate??
The number of radioactive decays per second for a radioactive source.
31
What is the unit of radioactive activity?
Becquerel (Bq)
32
Define the activity of an unstable nucleus.
Activity is the rate of decay of a source unstable nuclei.
33
What is the name of the process in which an unstable nucleus gives out radiation to become more stable?
Radioactive decay.
34
Why do unstable nuclei give out radiation?
• Unstable nuclei undergo decay to become more stable
• As they release radiation their stability increases
35
What did James Chadwick's experiments on the atom prove?
The existence of neutrons.
36
What reinforces a scientific theory?
When experimental results agree with the hypothesised theoretical calculations and theories.
37
State the conclusions of the Alpha-Scattering experiment.
• Most of the mass of the atom is concentrated at the centre in the nucleus
• The nucleus is positively charged
38
What is the name given to the currently accepted model of the atom?
The Bohr nucleur model
39
Which experiment led to the plum-pudding model being discarded?
Rutherford's alpha-scattering experiment.
40
Prior to the discovery of the electron what was believed about the atom?
The atom was believed to be indivisible.
41
How did the plum-pudding model describe the atom?
A ball of positive charge, with negatively charged electrons distributed evenly throughout it.
42
What may lead to a scientific model being changed or replaced?
The discovery of new experimental evidence which doesn't agree with the existing theory.
43
How do atoms turn into positive ions?
• They lose one or more of their outer electrons
• Electrons are negatively charged, so the resultant charge of the atom is positive
44
What is an isotope of an atom?
An atom of an element that has a different number of neutrons, but the same number of protons.
45
What is an atom's mass number?
The total number of protons and neutrons in the atom.
46
What is the name given to the number of protons in an atom?
Atomic Number
47
What do all forms of the same element have in common?
They all have the same number of protons.
48
How does the ratio of electrons to protons in an atom result in the atom having no overall charge?
• The number of protons is equal to the number of electrons
• Protons and electrons have equal and opposite charges, so charge cancels
49
Explain how an atom's electron arrangement changes when it emits EM radiation.
• Electrons move closer to the nucleus
• They move to a lower energy level
50
Give two ways that an atom's electron arrangement can be changed.
1. Absorbing electromagnetic radiation
2. Emitting electromagnetic radiation
51
What type of charge does the nucleus of an atom have? Why?
• Positive charge
The nucleus contains protons and neutrons
• Protons have a positive charge
• Neutrons have no charge
52
Describe the arrangement of protons, neutrons and electrons in an atom.
• The protons and neutrons are found in the atom's nucleus
• The electrons are found in discrete energy levels around the nucleus
53
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
54
Where is most of the mass of an atom concentrated?
In the nucleus
55
What are the three subatomic constituents of an atom?
1. Proton
2. Neutron
3. Electron
56
What is potassiums reaction with water?
- quicker reaction time compared to Na
- fizzed around the lilac flame was seen
- hydrogen gas was given off
57
What is sodium's reaction with water?
- quicker reaction time compared to Li
- fizzed around on the surface and rolled into ball
- hydrogen gas was given off
58
What is lithium's reaction with water?
- took a while to react
- fizzed around on the surface
- hydrogen gas was given off
59
What are some of the noble gases used for?
- helium is used in party balloons
- neon is used in advertising signs
- krypton is used in lasers designed for laser eye surgery
- argon is used in lightbulbs to stop the filament reacting with oxygen.
60
What is different about group 0
(The Noble Gases)
- the boiling points of the noble gases increase with increasing atomic mass (going down the group)
- don't form molecules because their full outer shell gives them a
"stable electron arrangement"
- very unreactive because they have full outer shells.
61
What are the differences of the development of the periodic table?
- Newlands said that every eight elements with similar properties, which Mendeleev state of the elements in group have similar properties.
- Mendeleev left gaps for the elements that he said that were not discovered yet; he was correct and left the correct gaps.
- The reaction that Newlands got was negative by other scientists, as Newlands grouped differently related elements together, while Mendeleev got a curious reaction, then that turned into a useful tool.
- Mendeleev swapped elements around if he thought they were in the wrong positions, while Newlands never changed any elements around.
62
What are the similarities of the development of the periodic table?
- both Newlands and Mendeleev ordered elements by their increasing atomic mass
- both scientists added all elements known at the time to their version of the table
- both scientist produced tables in which elements with similar properties were placed at regular intervals
63
What is the relative mass of an electron?
Very small
64
What is the relative mass of a neutron?
1
65
What is the relative mass of a proton?
1
66
What is the relative charge of an electron?
-1
67
What is the Nucleur model?
Positively charged alpha particles were fired at gold atoms. The majority of alpha particles pass straight through this provided the atom is mostly empty space. A tiny proportion of the alpha particles deflect back at large angles. This suggested that the atom had a tiny nucleus. Because the alpha particles are positive and were repelled by the nucleus, this means the nucleus also has a positive charge.
68
Who created the plum pudding model?
JJ Thomson
69
What did later experiments lead to the idea of?
Later experiments led to the idea that the positive charge of any nucleus can be subdivided into a whole number of smaller species each particle having the same amount of positive charge. The name proton was given to these particles.
70
What are the different physical seperation methods?
- filtration
- crystallisation
- simple distillation
- chromatography
- fractional distillation
71
How are mixtures separated?
Mixtures can be separated by physical processes, such as filtration, crystallisation, simple, distillation, fractional distillation and chromatography. These physical processes do not involve chemical reactions and no new substances are made.
72
What are the physical properties of group 1?
- soft - get softer going down the group.
- have relatively low melting points.
- have low densities.
73
What does it mean if an element has a full outer shell?
- they are unreactive
74
In group 0 what happens as you go down the group?
Going down the group boiling point increases because:
- atoms are larger.
- intermolecular forces between atoms increase.
- more energy is required to overcome them.
75
Which group has a full outer shell?
Group 0 - the noble gases
76
What is distillation?
Seperating mixtures of liquids of different boiling points.
77
What is crystillistion?
Seperating a soluble solid from a solution.
78
What is filtration?
Seperating an insoluble base from a liquid.
79
What did James Chadwick discover about neutrons?
- discovered particles with a mass but no charge.
- named these particles neutrons.
80
Who discovered neutrons?
James Chadwick
81
What did Niels Bohr discover about electron shells?
- determined that electrons are held in shells, or energy shells.
- determined that protons, with a positive charge, are in the nucleus of each atom.
82
Who discovered electron shells?
Neils Bohr
83
What did Ernest Rutherford conclude in the Nucleur model?
- the mass of an atom is concentrated in the centre of the atom - the nucleus.
- the nucleus is positively charged.
84
Who created the Nucleur model?
Ernest Rutherford
85
What is the Nucleur model?
- carried out the gold foil experiment.
- he fired positively charged alpha particles at a thin sheet of gold foil.
- expected all particles to go straight through.
- most did, but some scattered ir different directions.
86
What is the maximum electron configuration?
2,8,8
87
What does the number of electrons mean?
The atomic number
88
What does the number of neutrons mean?
[Number of neutrons = the atomic
number
89
What does the number of protons mean?
The atomic number
90
What does the bottom number on the periodic table elements mean?
- the smaller number is the atomic (proton) number
91
What does the top number on the periodic table elements mean?
- the larger number is the relative atomic mass (RAM).
92
What is the relative charge of an electron?
-1
93
What is the relative charge of a neutron?
0
94
What is the atomic mass of an electron?
1/1840
95
What is the atomic mass of a neutron?
1
96
What is the atomic mass of the proton?
1
97
What are the qualities of an atom?
- has a central nucleus surrounded by electrons arranged in shells.
- the nucleus comprises protons and neutrons.
- the nucleus is less 1/10,000 the overall size of an atom.
- the remaining space between the electron and nucleus is empty.
98
What is the relative atomic mass?
The number of protons and neutrons in an atom.
99
What is a proton?
A positively charged subatomic particle. Has a relative atomic mass of 1. In the nucleus of an atom.
100
What is the nucleus?
Found in the centre of an atom.
Compromises protons and neutrons (except hydrogen, which is just one proton and neutrons).
101
What is a neutron?
A neutrally charged subatomic particle. Has a relative atomic mass of 1. In the nucleus of the atom.
102
What is a mixture?
Two or more elements or compounds chemically bonded to one another.
103
What is an isotope?
A group of atoms with the same number of protons but different numbers of neutrons.
104
What is an ion?
An atom or group of atoms which has gained or lost electrons to become charged.
105
What is energy level (shells)?
Shells surrounding the nucleus that the electrons occupy.
106
What is an element?
A substance comprimising only one type of atom. Each atom has the same number of an atom.
107
What is an electron?
A negatively charged subatomic particle. Has a very small relative atomic mass. Orbits the nucleus of an atom.
108
What is a compound?
A substance with two or more elements chemical bonded to each other.
109
What is an atomic number?
Number of protons in an element.
110
What is an atom?
The smallest part of an element that can exist.
111
Why is alpha radiation the most ionising?
Alpha is the most ionising due to the fact it has the highest charge
112
Why is alpha radiation the most ionising?
Alpha is the most ionising due to the fact it has the highest charge.
113
What happens when atoms in
DNA become ionised?
Mutations and can lead to cancer.
114
What is contamination?
Contamination is when an object is mixed with a radioactive substance.
115
What is irradiation?
Irradiation is when a surface is exposed to radiation.
116
Before measuring the current rate of a radioactive source, what must you measure?
Background count rate
117
Why is the beta particle emitted?
An electron is created in the nucleus and instantly emitted.
118
What happens to the alpha particle emitted?
Two protons and two neutrons are emitted as an alpha particle.
119
In beta decay, what is the change in nucleus?
Neutrons in the nucleus turns into a proton.
120
In alpha decay, what is the change in nucleus?
Nucleus loses two protons and two neutrons.
121
Why did they call the centre of the atom a nucleus?
They called the centre the nucleus and knew it was positive because alpha particles which have a positive charge of 2+, meant that they will deflect off.
122
Why did they call the centre of the atom a nucleus?
They called the centre the nucleus and knew it was positive because alpha particles which have a positive charge of 2+, meant that they will deflect off.
123
Why did they call the centre of the atom the nucleus?
They called the centre the nucleus and knew it was positive because alpha particles which have a positive charge of 2+, meant that they will deflect off.
124
In Rutherford's scattering experiment, what did the deflected particles lead to?
Some were deflected through large angles - the plum pudding model cannot explain this. These reflections meant that the centre of an atom must consist of a positive charge.
125
What is one man-made source of radiation?
Nucleur Power Plants
126
What is one example of a natural source of background radiation?
- rocks
- food
- cosmic rays
127
What are the three types of radiation?
Alpha, Beta and Gamma.
128
[What is the type of particle found outside the nucleus?
Electrons
129
What is the description of gamma rays?
Waves with very high energies and short wavelengths.
130
What is the description for beta particles?
Is a stream of fast moving electrons.
131
What is the charge of neutrons?
Neutrons have no charge.
132
What is the nucleus made up of?
- Protons
- Neutrons
- No electrons
133
What are protons made up of?
Positive charge
134
What does the emission of a gamma ray cause?
The emission of a gamma ray does not cause the mass or the charge of the nucleus to change.
135
What does beta decay cause?
Beta decay does not cause the mass of the nucleus to change but does causes the charge of the nucleus to increase.
136
What does alpha decay cause?
Alpha decay causes both the mass and charge of the nucleus to decrease.
137
What is a beta particle represented by?
0
-1. e
138
What are gamma rays absorbed by?
Concrete
139
What are beta particles absorbed by?
Aluminium
140
What are alpha particles absorbed by?
Paper
141
What does the type of radiation emitted affect?
The type of radiation emitted affects the level of hazard.
142
What is the hazard of radioactive contamination?
The hazard from contamination is due to the decay of the contaminating atoms.
143
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms on other materials.
144
What is the half life of a radioactive isotope?
The half life of radioactive isotope is the time it takes from the number of nuclei of the isotope in a sample to half, all the time and takes on the count rate from a sample containing the isotope to fall to half its initial value.
145
Is radioactive decay random or programmed?
Radioactive decay is random.
146
How does the nucleus make the atomic nuclei more stable?
The nucleus gives out radiation as it changes to become more stable.
147
What did the experimental work of James Chadwick prove?
Experimental work of James Chadwick proved the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an adapted scientific idea.
148
What did later investigations of positive charge and the nucleus lead to?
Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.
149
How did Niels Bohr adapt the nuclear model?
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
150
What did the nuclear model replace?
The plum pudding model.
151
What are the results from the alpha particle scattering experiment lead to?
- the mass of an atom was concentrated at the centre.
- the nucleus was charged.
152
Before the discovery of the electron, what were atoms thought to be?
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
153
What happens to an atom if they lose one or more outer electrons?
Atoms turn into positive ions if they lose one or more outer electrons.
154
What is it called when atoms of the same element have different numbers of neutrons?
Atoms of the same element have different numbers of neutrons; these atoms are called isotopes of that element.
155
Is the atomic number the number at the top or the bottom?
Bottom
156
Is the mass number the number at the top or bottom?
Top
157
The total number of ____ and ____ in an atom is called its mass number.
Protons and Neutrons
158
What is the name of the number of protons in an element?
The number of protons in an atom of an element is called its atomic number.
159
All atoms of a particular element have the same number of ____.
Protons
160
What is the charge of an atom?
Atoms have no overall electrical charge.
161
Why may the electron arrangement move?
The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emissions of electromagnetic radiation (move closer to the nucleus; a lower energy level).
162
How are electrons arranged around the nucleus?
The electrons are arranged at different distances from the nucleus.
163
Where is the most of the mass of an atom concentrated?
In the nucleus.
164
Where is the most of the mass of an atom concentrated?
In the nucleus.
165
What is the radius of the nucleus?
The radius of the nucleus is less than 1/10,000 of the radius of an atom.
166
What is the basic structure of an atom?
| The basic structure of an atom is it a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.
167
What size are atoms?
Atoms are very small
168
What are all substances made up of?
All substances are made of tiny particles of matter called atoms which are the building blocks of all matter
169
Where are the protons and neutrons in the atom?
Located at the centre of the cell, in the nucleus.
170
Where do the electrons move?
The electrons move very fast around the nucleus in orbital paths called shells.
171
What is an element?
An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
172
Where are the elements found?
All the elements are found in the periodic table.
173
How many elements does the most recent periodic table contain?
The most recent Periodic Tables commonly contain around 103 elements although some go up to 118 elements.
174
What happens when elements take part in a chemical reaction?
Elements take part in chemical reactions in which new substances are made in processes that most often involve an energy change
175
What is a compound?
- A compound is a pure substance made up of two or more elements chemically combined and which cannot be separated by physical means.
176
What do ionic compounds contain?
Ionic compounds contain metal and non-metal elements joined together as particles called ions
177
What happens to the non-metal element?
- The non-metal element always takes on the name ending ‘– ide’ unless oxygen is also present.
- For example, PbS is called lead sulfide and MgCl2 is called magnesium chloride.
178
What happens in a compound when oxygen is present?
When oxygen is present the name ending is usually ‘-ate’
For example, CuSO4 is copper sulphate, KClO3 is potassium chlorate and Na2CO3 is sodium carbonate
179
What do covalent compounds contain?
Covalent compounds contain only non-metals
180
What are non-metals named using?
- They are named using prefixes (mono, di, tri, tetra, penta) to show how many of each element is present in the formula.
- For example, CO2 is carbon dioxide, NO is nitrogen monoxide and SiCl4 is silicon tetrachloride.
181
What does H2SO4 stand for?
Sulfuric Acid
182
What does NH3 stand for?
Ammonia
183
What does CH4 stand for?
Methane
184
What does HCl stand for?
Hydrochloric acid
185
What does C6H12O6 stand for?
Glucose
186
What does C2H5OH stand for?
Ethanol
187
What does HNO3 stand for?
Nitric acid
188
What do word equations show?
These show the reactants and products of a chemical reaction using their full chemical names
189
Where are the reactants found?
The reactants are those substances on the left-hand side of the arrow and can be thought of as the chemical ingredients of the reaction
190
Where are the new substances found?
The products are the new substances which are on the right-hand side of the arrow
191
What does a symbol equation show?
A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction
192
What happens to substances before and after chemical reactions?
New substances are made during chemical reactions.
- However, the same atoms are always present before and after reaction.
- They have just joined up in different ways.
- Atoms cannot be created or destroyed, so if they exist in the reactants then they absolutely must be in the products!
193
What is the total mass of reactants equal to?
Because of this the total mass of reactants is always equal to the total mass of products
194
What does the law of conservation of mass allow?
The Law of Conservation of Mass enables us to balance chemical equations, since no atoms can be lost or created
195
What do half equations show?
Half equations are used to show what happens to the electrons in reactions where atoms, molecules or ions are gaining or losing electrons.
196
Why are half equations called half equations?
- They are called half equations, because they represent only half of what is happening in a reaction involving electron transfer
- One species gains electrons
- Another species loses electrons
197
What are examples of half equations?
Pb2+ + 2e- → Pb
2Br- → Br2 + 2e-
198
What do ionic equations indicate?
Ionic equations are used to indicate what happens to ions during reactions
199
What do ionic equations help to do?
They help to simplify complicated processes where many substances are present, but only certain ions are actually reacting with each other
200
What are ions that are present but do not take part in the reaction called?
Spectator Ions
201
What do mixtures contain?
Mixtures can contain elements and / or compounds.
202
How are substances joined in a mixture?
- The parts of a mixture are not chemically bonded together and so they can be separated by physical means.
- The choice of the method of separation depends on the nature of the substances being separated
203
How is a mixture separated?
- All methods rely on there being a difference in a physical property such as the boiling point or solubility, between the substances being separated
204
How is filtration used?
- Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g., sand from a mixture of sand and water).
- Centrifugation and decanting can also be used for this mixture.
205
What are the steps to filtering something?
- A piece of filter paper is placed in a filter funnel above a beaker.
- A mixture of insoluble solid and liquid is poured into the filter funnel.
- The filter paper will only allow small liquid particles to pass through as filtrate.
- Solid particles are too large to pass through the filter paper so will stay behind as a residue.
206
What is crystallisation? How does it work?
- Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water).
207
How does crystallisation take place?
- The solution is heated which allows the solvent to evaporate and leaves a saturated solution.
- To test if the solution is saturated a clean, dry, cold glass rod is dipped into the solution.
- If the solution is saturated, crystals will form on the glass rod.
- The saturated solution is then allowed to cool slowly.
- Crystals begin to grow as solids come out of solution due to decreasing solubility.
- The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry.
208
What is simple distillation?
This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids.
209
How does simple distillation take place?
- The solution is heated and a liquid evaporates producing a vapour which rises through the neck of the round-bottomed flask (e.g. for saltwater, this would be water boiling at 100 oC).
- The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker.
- After all the liquid is evaporated from the solution, only the solid solute will be left behind.
210
What is fractional distillation?
This is used to separate two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two).
211
What are the steps to fractional distillation? 
- The solution is heated to the temperature of the substance with the lowest boiling point.
- This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker.
- All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture.
For water and ethanol
- Ethanol has a boiling point of 78 ºC and water of 100 ºC.
- The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker.
- When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated.
212
What is paper chromatography? 
This technique is used to separate substances that have different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink).
213
How is paper chromatography carried out?
1. A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples.
2. The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container.
3. The solvent travels up the paper by capillary action, taking some of the coloured substances with it.
4. Different substances have different solubilities so will travel at different rates, causing the substances to spread apart.
- Those substances with higher solubility will travel further than the others.
5. This will show the different components of the ink / dye
If two or more substances are the same, they will produce identical chromatograms.
6. If the substance is a mixture, it will separate on the paper to show all the different components as separate spots.
7. An impure substance will show up with more than one spot, a pure substance should only show up with one spot.
214
What is the equipment required for paper chromatography? 
- Chromatography paper
- Pencil
- Different inks
- Beaker
- Solvent
- Ruler
215
When did John Dalton present his atomic theory?
1803
216
What are the three key ideas John Dalton’s atomic theory was based on?
- Matter is made of atoms which are tiny particles that cannot be created, destroyed, or divided.
- Atoms of the same element are identical, and atoms of different elements are different.
- Different atoms combine together to form new substances.
217
When did Dalton “Billard Ball” Model come into existence?
1803
218
When did Thomson “PLUM PUDDING” Model come into existence?
1897
219
When did Rutherford model come into existence?
1909-1911
220
When did Niels “Bohr Model” come into existence?
1913
221
When did the Quantum mechanical model come into existence?
1926
222
In 1897, what did physicist JJ Thompson, discover? 
The electron
223
How did JJ Thompson discover the electron?
- Using a cathode-ray tube, he conducted an experiment which identified the electron as a negatively charged subatomic particle, hence proving that atoms are divisible.
224
What did JJ Thompson’s theory lead to?
- Based on his investigations, Thomson proposed a model of the atom known as the plum pudding model which depicted negative electrons spread throughout soft globules of positively charged material.
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What did Ernest Rutherford base his model off of?
In 1909, Ernest Rutherford presented his model of the atom based on the famous gold foil experiment
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What is the gold foil experiment?
Rutherford shot a beam of positively charged particles at a thin sheet of gold foil and based on the plum pudding model, expected the particles to pass through the foil because the positive charge of the nucleus was thought to be evenly spread out
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What happened to some of the particles shot at the gold foil?
Some particles were scattered, however, and a few were deflected directly back, which led him to postulate that most of an atom's mass is concentrated in a region of space at the centre of the atom called the nucleus
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Was Rutherford scattering idea similar to the plum pudding model?
The results of Rutherford’s scattering experiments did not support the idea that atoms were as described in the plum pudding model, so the model had to be changed.
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What does Rutherford’s model consist of?
In Rutherford's model, the atom consists mainly of empty space with the nucleus at the centre and the electrons orbiting in paths around the nucleus.
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What was Rutherford’s scattering model known as?
- This model was known as the nuclear model of the atom.
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What is the difference between the Plum Pudding Model and Rutherford Scattering experiment?
- In the plum pudding model, atoms were described as being made from electrons embedded within a positive sphere, whereas in the nuclear model the nucleus is a positive structure at the centre of the atom, with negative (and much smaller) electrons ‘orbiting’ around the outside of it.
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What does the Bohr Model show?
- In 1913, Niels Bohr further developed the nuclear model by proposing that electrons orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus.
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In the Bohr Model, what does each orbital have?
- Each orbital has a different energy associated with it, with the higher energy orbitals being located further away from the nucleus.
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What did the Bohr model solve?
This model solved the question of why the atom does not collapse inwards due to the attraction between the positive nucleus and negative electrons circling the nucleus.
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What did Bohr’s theory agree with?
Bohr’s theory and calculations agreed with experimental results
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What did further investigation of the Bohr Model lead to?
- Further investigation and experimentation revealed that the nucleus could be divided into smaller particles, each one having the same mass and charge.
- This work led to the discovery of the proton.
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What did Rutherford put forward in 1920?
- In 1920, Rutherford put forward the idea of the existence of large, neutral particles within the nucleus.
- His idea was based on the differences between the atomic mass and the atomic number of atoms.
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What did James Chadwick publish in 1932?
In 1932, James Chadwick published a paper based on an experiment carried out by Frédéric and Irène Joliot-Curie which provided evidence for the existence of these neutral particles which were called neutrons.
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What charge do atoms have overall?
- Atoms are neutral overall.
- Even though they contain charged subatomic particles, the charges cancel each other out in an atom.
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What are the size of atoms?
Atoms are extremely small with a radius of about 1 x 10^-10 metres or 0.1 nanometres
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What size is the radius of the nucleus?
- The radius of the nucleus is about 10 000 times smaller than that of the atom, around 1 x 10-14 m, so it is an extremely small region of space compared to the overall size of the atom.
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What is the mass of electrons?
- Electrons have a much smaller mass than protons and neutrons (1 proton has the same mass of around 1840 electrons) and move in the space outside the nucleus in orbits.
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What is the atomic number?
The atomic number or proton number is the number of protons in the nucleus of an atom.
- It is also the number of electrons present in an atom and determines the position of the element on the periodic table.
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Why is the proton number unique?
The proton number is unique to each element, so no two elements have the same number of protons
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What happens to electrons?
Electrons can be lost, gained, or shared during chemical processes but the proton number of an atom does not change in a chemical reaction.
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What does mass mean?
MASS = MASSIVE
- mass number is always the bigger of the two numbers, the other smaller one is thus the atomic / proton number.
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What is the mass number?
The mass number (or nucleon number) is the total number of protons and neutrons in the nucleus of an atom
The symbol for this number is A
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How do you find the number of neutrons in an atom?
- The nucleon number minus the proton number gives you the number of neutrons of an atom.
- Note that protons and neutrons can collectively be called nucleons.
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What are isotopes?
- Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons.
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What do isotopes display?
- Isotopes display the same chemical characteristics.
- This is because they have the same number of electrons in their outer shells, and this is what determines their chemistry.
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What is the difference between isotopes?
- The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only.
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Can isotopes be two different elements?
For atoms to be isotopes of each other, they must both be from the same element, hence they must have the same atomic number. E.g., C-13 and C-14 are isotopes whereas C-13 and H-2 are not.
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What is the atomic number equal to?
Atomic number = Protons
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What do atoms have the same number as?
Since atoms are neutral, then it is also the same as the number of electrons (e).
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What is the mass number made up of?
- The mass number is the number of protons plus neutrons.
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How can the number of neutrons be calculated?
- The number of neutrons (n) can thus be calculated by subtracting the atomic number from the mass number.
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What is relative atomic mass used for?
- Atoms are so tiny that we cannot really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass (Ar) is used.
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What is the relative atomic mass equal to?
- The relative atomic mass unit is equal to 1/12th the mass of a carbon-12 atom.
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How do you calculate Ar?
Ar = (% of isotope A x mass of isotope A) + (% of isotope B x mass of isotope B) / 100
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What is the electrons role in the atom?
- Electrons orbit the nucleus in shells.
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Was each shell the same?
- Each shell has a different amount of energy associated with it.
- The further away from the nucleus, the more energy a shell has.
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What happens when the shell becomes full of electrons?
- When a shell becomes full of electrons, additional electrons have to be added to the next shell.
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What is the electron shell configuration?
- 2 electrons …
- 8 electrons …
- 8 electrons …
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What is the outermost shell called?
- The outermost shell of an atom is called the valence shell and an atom is much more stable if it can manage to completely fill this shell with electrons.
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What happens if the outer shell is not filled?
- In most atoms, the outermost shell is not full and therefore these atoms react with other atoms in order to achieve a full outer shell of electrons (which would make them more stable).
- In some cases, atoms lose electrons to entirely empty this shell so that the next shell below becomes a (full) outer shell.
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What is a period?
The red numbers at the bottom show the number of notations which is 3, showing that a chlorine atom has 3 shells of electrons
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What is a group?
The last notation, in this case 7, shows that chlorine has 7 outer electrons, and therefore is in group 7
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How are the elements in the periodic table arranged?
- Elements are arranged on the periodic table in order of increasing atomic number.
- Each element has one proton more than the element preceding it.
- This is done so that elements end up in columns with other elements which have similar properties.
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What is a period and an example?
- Period: These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7.
- E.g. elements in period 2 have two electron shells, elements in period 3 have three electron shells.
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What is a group? What is an example?
- Group: These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 – 7, with a final group called group 0 (instead of group 8).
- E.g. group 4 elements have atoms with 4 electrons in the outermost shell, group 6 elements have atoms with 6 electrons in the outermost shell and so on.
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What does the group number indicate?
- The group number of an element which is given on the Periodic Table indicates the number of electrons in the outer shell (valence electrons).
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What can we use the group number to do?
- We can use the group number to predict how elements will react as the number of valence shell electrons in an element influences how the element reacts.
Therefore, elements in the same group react similarly.
- By observing the reaction of one element from a group, you can predict how the other elements in that group will react.
- By reacting two or more elements from the same group and observing what happens in those reactions you can make predictions about reactivity and establish trends in reactivity in that group.
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What happens to the group 1 metals as you go down the group?
The group 1 metals become more reactive as you move down the group while the group 7 halides show a decrease in reactivity moving down the group.
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What does “periodic” mean?
The word “periodic” is used in the name of the Periodic Table as similar properties appear in elements placed at regular intervals throughout the table.
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What name is given to different atoms chemically bonded in a fixed ratio?
A compound.
