Flashcards in C4 Deck (132):
When and what was John Dalton's theory?
In 1800, he proposed the theory that all atoms of the same element were the same.
When and what was J.J.Thomson's discovery?
In the late 1890s, he discovered the electron
When and what was Ernest Rutherford's discovery?
In 1911, he discovered that the atom had a dense centre called the nucleus.
When and what was Niels Bohr's prediction?
In 1913, he predicted that electrons occupy orbitals.
What have some unexpected results from scientists such as Geiger and Marsden led to?
The model of the atom being modified in order to explain them
What is the structure of an atom?
An atom has a central nucleus surrounded by shells of negatively charged electrons. The nucleus is made up of protons and neutrons. The nucleus is positively charged but the atom has no overall charge.
Why does an atom have no overall charge?
Because it has the same number of (positive) protons and (negative) electrons, so the charges cancel each other out
What are the dimensions of an atom?
Atoms have a radius of about 1^-10m and a mass of about 10^-23g
What is the relative charge of a proton?
What is the relative charge of a neutron?
What is the relative charge of an electron?
What is the relative mass of a proton?
What is the relative mass of a neutron?
What is the relative mass of an electron?
What is an element?
An element is made of one type of atom. Elements can't be chemically broken down. There are just over 100 naturally occurring elements
What is a compound?
A compound is a substance made of two or more elements that are chemically combined. You can identify the elements in a compound from its formula, using the periodic table.
What is the mass number?
The total number of protons and neutrons in an atom. It's the bigger of the two numbers next to the element symbol.
What is the atomic number?
The total number of protons in an atom. It's the smaller of the two numbers next to the element symbol.
How are the elements in the periodic table arranged?
In increasing atomic number
What can you use the periodic table to find?
An element from its atomic number, and the atomic number of an element
What is the group number the same as?
The number of electrons in the outer shell of an element's atom.
What is the period number the same as?
The number of occupied shells that an element's atom has
What do you need to be able to work out the number of protons, electrons and neutrons in an atom?
The atomic number, mass number and charge
What are isotopes?
Atoms of the same element that have the same atomic number but a different mass number
What are the similarities and the difference between isotopes?
They have the same number of protons and electrons, but a different number of neutrons.
What does electron configuration tell you?
How the electrons are arranged around the nucleus in shells. The first shell can hold a maximum of 2 electrons, and the second and outer shell have a maximum of 8.
What is an ion?
A charged atom or group of atoms.
How is a positive ion made?
When an atom, or group of atoms, loses one or more electrons.
How is a negative ion made?
When an atom, or group of atoms, gains one or more electrons.
What happens in ionic bonding?
The metal atom loses all outer-shell electrons to become a positive ion, the non-metal atom gains electrons to fill its outer shell and become a negative ion. The positive and negative ions are attracted to each other. This attraction is an ionic bond.
When can the two ionically bonded compounds, sodium chloride and magnesium oxide, conduct electricity. They don't conduct electricity when solid because the ions are held in place and can't move, and both have high melting points.
They both dissolve in water, and can conduct electricity when in solution because the charged ions are free to move about. Both can also conduct electricity when molten because the charged ions are free to move about.
Sodium chloride and magnesium oxide form giant ionic lattices in which positive and negative ions are strongly attracted to each other. What does this mean?
It means that they have high melting points as there is a strong attraction between oppositely charged ions. They can conduct electricity when molten or in solution because the charged ions are free to move about. They don't conduct electricity when solid because the ions are held in place and can't move.
Why does magnesium oxide have a higher melting point than sodium chloride?
Because the ionic bonds are stronger and need more energy to be broken.
When a metal and a nonmetal combine, what happens?
Electrons are transferred from one atom to the other, forming ions. Each ion will have a complete outer shell.
What is a stable octet?
A complete outer shell
What do ions with different charges combine to form?
Ionic compounds, which have equal amounts of positive and negative charge.
What is a vertical column of elements in a periodic table called?
Why do elements in the same group in the periodic table have similar chemical properties?
Because they have the same number of electrons in their outer shell.
What is a horizontal row of elements in a periodic table called?
What is the period for an element related to?
The number of occupied electron shells it has.
If you are given an element's electronic structure, how do you find its position in the periodic table?
Example: sulfur's structure is 2.2.6, so it has three electron shells and six electrons in its outer shell. So, it can be found in the third period and in Group 6
What are the three types of bonding?
Ionic, covalent and metallic
What are ionic bonds between?
metals and non-metals
What are covalent bonds between?
What are metallic bonds between?
What is covalent bonding?
It's when non-metals combine by sharing pairs of electrons. Water and carbon molecules are both covalently bonded molecules.
Why do simple covalently bonded molecules have low melting points?
Because they have weak intermolecular forces of attraction between molecules.
Why don't simple covalently bonded molecules conduct electricity?
Because there aren't any free electrons
How is the simple covalently bonded molecule, hydrogen, formed?
the two hydrogens share a pair of electrons
How is the simple covalently bonded molecule, chlorine, formed?
the two chlorine atoms share a pair of electrons
How is the simple covalently bonded molecule, methane, formed?
the carbon atom shares a pair of electrons with each hydrogen atom
How is the simple covalently bonded molecule, carbon dioxide, formed?
The outer shells of the carbon and oxygen atoms overlap. The carbon atom shares two pairs of electrons with each oxygen atom to form a double covalently bonded molecule
What did Dobereiner do?
He was the first to suggest a 'Law of Triads', where he grouped the elements into sets of three with similar properties. The middle element would have the average mass of the other two elements. However, not all the elements were known, and the patter did not work for every known element.
What did John Newlands do?
He was the first scientist to make a table of elements, which he called the 'Law of Octaves', where every eighth element behaved the same. But, he included some compounds in his table, as he believed them to be elements.
What did Mendeleev do?
He was the author of the modern periodic table. He left gaps in his table for the unknown elements, and made predictions about their properties. His predictions were later proved correct. Also, investigations on atomic structure agreed with his ideas.
Where in the periodic table are the alkali metals found?
In group 1.
Why are alkali metals stored under oil?
Because they react with air, and react vigorously with water
What do alkali metals produce when reacted with water?
hydrogen, and a hydroxide.
Why are alkali metals known as such?
Because they are soluble and form alkaline solutions
How does lithium react with water?
How does sodium react with water?
More aggressively than lithium
How does potassium react with water?
It melts and burns with a lilac flame
How should you recognise lithium and potassium compounds?
with a flame test
How do you carry out a flame test to recognise lithium and potassium compounds?
-A piece of clean nichrome wire is dipped in water.
-The wire is dipped in the solid compound (sample). The wire is then put into a bunsen flame.
-Each compound will produce a different coloured flame
Which colour does lithium burn?
Which colour does sodium burn?
Which colour does potassium burn?
How does rubidium react with water?
It is very fast, exothermic (gives out energy) and violent. If it's carried out in a glass beaker, the beaker may shatter.
As you go down group 1, what can be observed?
Density increases as you go down, with the exception of potassium.
Why do alkali metals have similar properties?
Because as they react, each atom loses one electron from its outer shell. So, a positive ion with a stable electronic structure is made.
Why do alkali metals get more reactive the further you go down the group?
Because the outer shell gets further away from the positive attraction of the nucleus. This makes it easier for an atom to lose an electron from its outer shell
What is the equation for the formation of sodium?
Na -> Na+ + e-
What is the equation for the formation of potassium?
K -> K+ + e-
How can you tell whether or not oxidation has taken place by looking at the ionic equation for a reaction?
Oxidation involves the loss of electrons by an atom, and as such, if the ionic equation shows that an electron has been lost, an oxidation reaction took place
What are the five non metals in Group 7 known as?
Which elements are the halogens (That are needed for GCSE)?
Fluorine, chlorine, bromine and iodine
At room temperature, what is chlorine?
A green gas
At room temperature, what is bromine?
An orange liquid
At room temperature, what is iodine?
A grey solid
What is iodine used as?
An antiseptic to sterilise wounds
What is chlorine used for?
To sterilise water, to make pesticides, and to make plastics.
Halogens react vigorously with alkali metals. What do they form?
Which is the most reactive halogen?
Which is the least reactive halogen?
What does a more reactive halogen do to a less reactive halogen in an aqueous solution of its metal halide?
It displaces it. For example, chlorine will displace bromides and iodides. Bromine will displace iodides.
If chlorine gas was passed through an aqueous solution of potassium bromide, what would be the product of the reaction?
Potassium chloride and bromine
If chlorine gas was passed through an aqueous solution of potassium iodide, what would be the product of the reaction?
Potassium chloride and iodine
If bromine was passed through an aqueous solution if potassium iodide, what would be the product of the reaction?
Potassium bromide and iodine
Which element is the halogen which will displace al of the other halogens from an aqueous solution of their metal halides?
Fluorine, because it's the most reactive element in group 7
What is Astatine?
A semi-metallic, radioactive element, and only very small amounts are found naturally. It's the least reactive of the halogens, and so, theoretically, it would be unable to displace any of the other halogens from a solution of their metal halides
As astatine is very unstable and difficult to study, how is information about it gathered?
The information is estimated by looking at the trend in boiling point, melting point and density as you go down group 7
Why do the halogens have similar properties?
Because, as they react, each atom gains one electron to form a negative ion with a stable electronic structure.
What does reduction involve?
The gain of electrons by an atom
Why are the halogens at the top of group 7 more reactive than those at the bottom of the group?
Because the outer shell is closer to the positive attraction of the nucleus, which makes it easier for an atom to gain an electron.
How can you, by looking at an equation of a reaction, determine whether it is oxidation or reduction?
If electrons are added, it's a reduction reaction. If electrons are taken away, it's an oxidation reaction.
What is an easy way to remember the definitions of oxidation and reduction?
OILRIG: Oxidation Is Loss of electrons, Reduction Is Gain of electrons
What are the transition metals?
A block of metallic elements between Groups 2 and 3 of the periodic table.
What colour are copper compounds?
What colour are iron[II] compounds?
What colour are iron[III] compounds?
Give two examples of transition metals being used as catalysts.
Iron is used in the Haber process. Nickel is used in the manufacture of margarine.
What is thermal decomposition?
A reaction where a substance is broken down into two or more substances by heating
What happens when transition metal carbonates are heated?
A colour change happens. They decompose to form a metal oxide and carbon dioxide.
What is the test for carbon dioxide?
It turns limewater milky
What is precipitation?
The reaction between solutions that makes an insoluble solid, which is known as a precipitate.
Why is iron used to make steel?
Because steel is used to make cars and bridges because it is very strong
Why is copper used to make electrical wiring?
Because it's a good conductor
Give an example of a metal being used because it is lustrous.
Gold is used in jewellery
Give an example of a metal being used because it is hard and has a high density.
Steel is used to make drill parts
Give an example of a metal being used because it has a high tensile strength.
Steel is used to make bridge girders
Give an example of a metal being used because it has high melting and boiling points.
Tungsten is used to make light-bulb filaments
Give an example of a metal being used because it is a good conductor of heat and electricity.
Copper is used to make pans and wiring
Metal atoms are packed very close together in a regular arrangement. How are the atoms held together?
By metallic bonds
Why do metals have high melting and boiling points?
The metal is held together by strong forces called metallic bonds. These are the electrostatic attractions between the metal ions and the delocalised electrons. So, the metals have high melting and boiling points
How is it that metal can conduct electricity?
Metal crystals are made from closely packed positive metal ions in a 'sea' of delocalised electrons. The free movement of the electrons allows the metal to conduct electricity
At low temperatures, some metals can become superconductors. What are these?
Superconductors have little, or no, resistance to the flow of electricity.
What are superconductors useful for?
Their low resistance is useful for powerful electromagnets [e.g. inside medical scanners], very fast electronic circuits [e.g. in a supercomputer] and for power transmission that doesn't lose energy
Why is there a need to develop superconductors that will work at room temperature?
They only work at temperatures below -200°c. This very low temperature is costly to maintain and impractical for large scale use
What are the four main sources of water in the UK?
rivers, lakes, reservoirs and aquifers [wells and boreholes]
What is water used for in the chemical industry?
As a coolant, as a solvent, and as a raw material.
Why is it important to conserve and not waste water in Britain?
Because, in some parts of Britain, the demand for water is higher than the supply
Why does water have to be treated to purify it and make it safe to drink?
Because untreated [raw] water can contain: insoluble particles, pollutants, microorganisms and dissolved salts and minerals
What are the 3 steps in the water treatment process?
Sedimentation- the water settles to allow the insoluble particles to sink.
Filtration- to remove the very fine particles
Chlorination- to kill the microorganisms in the water
Why is drinking water out of sea water currently an unrealistic option in the UK?
The equipment and energy needed to distil sea water is very expensive, racking up too high a cost.
To obtain pure water, what must happen, and why?
Tap water isn't pure- it contains soluble materials that aren't removed by the normal water treatment process. Some of these materials may be poisonous, so extra steps need to be taken to remove them. It must be distilled.
Name three pollutants that can be found in water supplies and are difficult to remove, and state where they come from.
Nitrates- from the run-off fertilisers, lead compounds- from old pipes in the plumbing, pesticides- from spraying crops near to the water supply.
Why are the dissolved ions of some salts easy to identify?
They will undergo precipitation reactions, which occur when an insoluble solid is made from mixing two solutions together
How can sulphates be detected?
By using barium chloride solution; a white precipitate of barium sulphate forms.
How are halide ions [the ions made by the halogens] detected?
With silver nitrate solution
With silver nitrate, what do chlorides form?
A white precipitate
With silver nitrate, what do bromides form?
A cream precipitate