Unit 1. Model of an atom

Question 1

What is an atom

Answer 1

The smallest part of an element that can exist

Question 2

What’s an atom made of

Answer 2

Each atom is made of subatomic particles called protons, neutrons, and electrons

Question 3

Where are the protons and neutrons located

Answer 3

The protons and neutrons are located at the centre of the atom, which is called the nucleus

Question 4

Where are the electrons

Answer 4

The electrons move very fast around the nucleus in orbital paths called shells

Question 5

What is the mass of an electron

Answer 5

The mass of the electron is negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located

Question 6

What is an element

Answer 6

An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.

Question 7

Where is the atomic mass and where is the atomic number

Answer 7

Atomic mass is top and atomic number is bottom

Question 8

What is a compound

Answer 8

A compound is a pure substance made up of two or more elements chemically combined and which cannot be separated by physical means

Question 9

What happens to the atoms

Answer 9

In these reactions atoms combine together that will give them full outer shells of electrons

Question 10

What does the chemical formula tell you

Answer 10

chemical formula is what tells you the ratio of atoms in a compound

Question 11

What is an ionic compound

Answer 11

Ionic compounds contain metal and non-metal elements joined together as particles called ions

Question 12

What is a covalent compound

Answer 12

Covalent compounds contain only non-metals

Question 13

How do you write a word equation

Answer 13

Word equations show the reactants and products of a chemical reaction using their full chemical names

Question 14

Which side are the reactants and which are the products

Answer 14

The reactants are those substances on the left-hand side of the arrow
They can be thought of as the chemical ingredients of the reaction
They react with each other to form new substances, which are the products
The products are on the right-hand side of the arrow
The arrow (which is spoken as “to form” or “produces”) implies the conversion of reactants into products
Reaction conditions or the name of a catalyst (a substance added to make a reaction go faster) can be written above the arrow

Question 15

How do you write a balance equation

Answer 15

When balancing equations, there must be the same number of atoms of each element on either side of the equation

Question 16

Here is a question

When magnesium oxide, MgO, reacts with nitric acid, HNO3, it forms magnesium nitrate, Mg(NO3)2, and water. Write a symbol equation for this reaction.

Answer 16

The balanced symbol equation is:
MgO (s) + 2HNO3 (aq) ⟶ Mg(NO3)2 (aq) + H2O (l)

Step 1 - writing the unbalanced equation
Magnesium oxide, MgO, reacts with nitric acid, HNO3, it forms magnesium nitrate, Mg(NO3)2, and water
MgO + HNO3 ⟶ Mg(NO3)2 + H2O
The Mg and O atoms (not including the O in the NO3 group appear to be balanced), so we should focus on the H atoms and NO3 groups
Step 2 - balancing hydrogen atoms
There are 2 hydrogen atoms on the product side, so 2 hydrogen atoms are needed on the reactant side
This means that 2 HNO3 will be needed as we cannot change the chemical formula
MgO + 2HNO3 ⟶ Mg(NO3)2 + H2O
This also balances the nitrate, NO3, groups
Step 3 - checking the equation
The equation appears balanced so we need to check that it is
Reactant side:
1 Mg atom
1 O atom - not including those in the NO3 group
2 H atoms
2 NO3 groups - remember to keep groups as a single entity if they are unchanged on both sides of the equation
Product side:
1 Mg atom
2 NO3 groups - remember to keep groups as a single entity if they are unchanged on both sides of the equation
2 H atoms
1 O atom - not including those in the NO3 group
The equation is now balanced

Question 17

What is a half-equation

Answer 17

Half equations are used to show what happens to the electrons in reactions where atoms, molecules or ions are gaining or losing electrons

Here is an example:
2Br- → Br2 + 2e-

The e represents ‘electrons’

Question 18

What is an ionic equation

Answer 18

Ionic equations are used to indicate what happens to ions during reactions

Question 19

Here is a question on ionic equations

For example, we can use ionic equations to show what happens when an acid neutralises and an alkali:
HCl + NaOH → NaCl + H2O

Answer 19

Written out as an ionic equation would be
H+ + OH- → H2O

This is because sodium and chloride ions were present at the beginning and also at the end of the reaction, so they are unchanged
Ions which are present but do not take part in reactions are called spectator ions

Question 20

What is a mixture

Answer 20

A mixture is a combination of two or more substances that are not chemically joined together
These substances can be elements and / or compounds

Question 21

Do mixtures need to be chemically joined

Answer 21

Mixtures can be just elements, just compounds or elements and compounds, but the substances must not be chemically joined together

Question 22

What does this mean

Answer 22

This means that mixtures can be easily separated by physical processes

Question 23

Name all processes

Answer 23

Filtration
Evaporation
Distillation
Chromatography

Question 24

How does filtration work

Answer 24

Filtration is used to separate an insoluble solid from a mixture of the solid and a liquid / solution
For example, sand from a mixture of sand and water

Question 25

Bullet point the method on filtration

Answer 25

Method A filter paper is placed in a filter funnel above a beaker The mixture of insoluble solid and liquid is poured into the filter funnel The filter paper will only allow liquid particles and soluble solids to pass The liquid that passes through into the beaker is called the filtrate Insoluble solids do not pass through the filter paper and are left behind as a residue

Question 26

How does crystallisation work

Answer 26

This method is used to separate a dissolved solid from a solution A simple application of this is to heat a solution to boiling, remove the heat and leave the solvent to evaporate

Question 27

Method of crystallisation

Answer 27

A simple application of this is to heat a solution to boiling, remove the heat and leave the solvent to evaporate This is when the solid is more soluble in hot solvent than in cold, e.g. copper sulphate from a solution of copper(II) sulphate The solution is heated, allowing the solvent to evaporate and leaving a saturated solution behind You can test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution If the solution is saturated, crystals will form on the glass rod when it is removed and allowed to cool The saturated solution is allowed to cool slowly Solids will come out of the solution as the solubility decreases This will be seen as crystals growing The crystals are collected by filtration They are then washed with distilled water to remove any impurities Finally, they are allowed to dry Common places to dry crystals are between sheets of filter paper or in a drying oven

Question 28

What is distillation

Answer 28

Distillation is used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids

Question 29

Method of distillation

Answer 29

The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask The vapour passes through the condenser, where it cools and condenses, turning into pure water which is collected in a beaker After all the water is evaporated from the solution, only the solid solute will be left behind Simple distillation can be used to separate the products of fermentation, such as alcohol and water However, fractional distillation is a more effective separation technique, commonly used when the boiling points of the liquids are close and/or a higher degree of purity is required, such as crude oil

Question 30

What is chromatography

Answer 30

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)

Question 31

What did John dalton discover in 1803

Answer 31

In 1803, John Dalton presented his atomic theory based on three key ideas: 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 At the time, the theory was correct but as science developed some parts of Dalton's theory were disproved This is a fundamental feature of science: new experimental evidence may lead to a scientific model being changed or replaced

Question 32

What is the plum pudding model?

Answer 32

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 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 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

Question 33

What did Rutherford's scattering experiment show?

Answer 33

In 1909, Ernest Rutherford presented his model of the atom based on the famous 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 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 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 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 This model was known as the nuclear model of the atom

Question 34

What is the Bohr model?

Answer 34

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 Each orbital has a different energy associated with it, with the higher energy orbitals being located further away from the nucleus 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 Bohr’s theory and calculations agreed with experimental results 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

Question 35

When was the neutron discovered?

Answer 35

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 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

Question 36

How big is an atom?

Answer 36

Atoms are extremely small with a radius of about 1 x 10-10 metres or 0.1 nanometres The central nucleus contains protons and neutrons only which are packed close together in a small region of space 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 This means that rather than being evenly spread out throughout the atom, virtually all of the atom's mass is concentrated inside the nucleus 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

Question 37

What is the atomic number of an atom?

Answer 37

The atomic number (or proton number) is the number of protons in the nucleus of an atom The symbol for this number is Z It is also the number of electrons present in an atom and determines the position of the element on the periodic table The proton number is unique to each element, so no two elements have the same number of protons Electrons can be lost, gained, or shared during chemical processes but the proton number of an atom does not change in a chemical reaction

Question 38

What is the mass number of an atom?

Answer 38

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 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 The atomic number and mass number for every element is on the periodic table

Question 39

What is an isotope?

Answer 39

Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number So, C-14 is the isotope of carbon which contains 6 protons and 6 electrons, but the 14 signifies that it has 8 neutrons (14 - 6 = 8) It can also be written as 14C 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 The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only

Question 40

What is relative atomic mass?

Answer 40

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 The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element The relative atomic mass unit is equal to 1/12th the mass of a carbon-12 atom All other elements are measured by comparison to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units For example, hydrogen has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon

Question 41

How to calculate relative atomic mass (Ar)

Answer 41

The relative atomic mass of each element is calculated from the mass number and relative abundances of all the isotopes of a particular element