Chemistry

GCSE

Atom

The smallest neutral part of an element that can take part in chemical reactions.

Element

A substance made up of only atoms with the same number of protons in the nucleus.

Atom

The smallest neutral part of an element that can take part in chemical reactions.

Element

A substance made up of only atoms with the same number of protons in the nucleus.

atomic number

The number of protons in the nucleus of an atom (symbol Z). Also known as the proton number.

mass number

The total number of protons and neutrons in the nucleus of an atom (symbol A). Also known as the nucleon number.

periodic table

Chart in which the elements are arranged in order of increasing atomic number.

Ar

Symbol for relative atomic mass (RAM).

isotopes

Atoms of an element with the same number of protons (atomic number) but different mass numbers due to different numbers of neutrons.

mean

An average calculated by adding up the values of a set of measurements and dividing by the number of measurements in the set.

nuclear fission

The reaction in which the nucleus of a large atom, such as uranium, splits into two smaller nuclei.

relative atomic mass (RAM)

The mean mass of an atom relative to the mass of an atom of carbon-12, which is assigned a mass of 12. The RAM of an element is the mean relative mass of the isotopes in the element.

Chemical property

How a substance reacts with other substances.

Dmitri Mendeleev

A Russian chemist that constructed a table that lead to the periodic table we know today.

Periodic table

An ordered list of all known elements.

Physical property

A description of how a material behaves and responds to forces and energy. Hardness is a physical property.

Prediction

What you think will happen in an experiment and why you think this.

Relative atomic mass, Ar

The Ar of an element is the mean relative mass of the isotopes in the element.

Group

A vertical column of elements in the periodic table. Elements in the same group generally have similar properties and the same electrons in outer shell.

Henry Mosley

The scientist who discovered that atomic number was equal to the number of positively charged particles (protons) in a nucleus of an atom.

inert

Does not react.

period

A horizontal row in the periodic table.

relative atomic mass

The mean mass of an atom compared to 1/12th the mass of an atom of carbon-12. (One atom of carbon-12 has been assigned a mass of 12.)

X-ray

Electromagnetic radiation that has a shorter wavelength than UV but longer than gamma rays.

electron

Tiny particle with a negative charge that is found in shells around the nucleus of an atom.

electron shell

Areas around a nucleus that can be occupied by electrons, usually drawn as circles. Also called an electron energy level.

electronic configuration

The arrangement of electrons in shells around the nucleus of an atom.

Chemical Properties

Mendeleev ordered his Periodic table by _ __

Physical Properties

The modern Periodic table is ordered by _ __

Outer

The group number of an element tells the number of electrons on the _ shell

Group

The _ number of an element tells the number of electrons on the outer shell

Period

The _ number of an element tells the number of shells

Shells

The period number of an element tells the number of

2

The first 20 elements can contain up to _ electrons on the first shell

8

The first 20 elements can contain up to _ electrons on the second shell

Explain the classification of alkali metals, halogens and noble gases, into groups in the periodic table.

The elements placed in each of these groups have similar chemical properties to the elements also in the same group as them. Alkali metals all form +1 ions, halogens always form -1 ions and noble gases are all inert. Their similar electronic configuration means they all react in similar ways.

Describe the main physical properties of alkali metals.

• Soft and can be cut with a knife.

• Low density (eg: Lithium, sodium and potassium float on water).

• Low melting and boiling points.

• Good conductors of heat and electricity.

• Shiny when freshly cut.

• Stored in oil so they don't react with oxygen + water in the air.

Describe the reactions of lithium, sodium and potassium with water.

Lithium and water= Bubbles fiercely on the surface of the water.

Sodium and water = Melts into a ball and fizzes about the surface.

Potassium and water = Bursts into flames and flies about the surface.

Describe the pattern of reactivity of the alkali metals.

Reactivity increases as you go down the group.

How does the electronic configurations of atoms of alkali metals affect their reactivity?

The further away the valence electron gets from the nucleus, the more reactive the element (as alkali metals get more reactive down the group, because the valence electron gets further away from the nucleus and is less strongly attracted to the nucleus + can be lost easily).

Recall the appearance of chlorine, bromine and iodine at room temperature.

Chlorine: Pale green gas

Bromine: Dark orange liquid

Iodine: Dark grey solid

Describe the trends in colour, melting point and boiling point of chlorine, bromine and iodine down the group, and use these to predict physical properties of other halogens.

Chlorine: Pale green gas,

Bromine: Dark orange liquid

Iodine: Dark grey solid

• Boiling and melting point increases down the group.

• Decreasing reactivity down the group.

• Colour gets darker down the group.

• Non-metals and brittle and crumbly when solid.

• Poisonous + smelly + toxic.

So after iodine (Astatine - expect a really dark, brittle, crumbly solid, with a lower reactivity and with higher melting and boiling points than iodine).

Describe the chemical test for chlorine gas.

• Use damp blue litmus paper.

• Chlorine gas (if present) dissolves in the water on the damp blue litmus paper and reacts with the litmus dye.

• The litmus paper first turns red as chlorine is acidic.

• The chlorine then bleaches the paper white.

Describe the reaction between a metal and a halogen.

Metal + Halogen = Metal Halide (salts)/ionic compounds.

Describe the reaction between hydrogen and a halogen.

Hydrogen + Halogen = Hydrogen Halide.

Describe hydrogen halides and their chemical properties.

• Compound of hydrogen and a halogen.

• Dissolve in water to form acidic solutions.

• Explosive reaction (covalent bonds between hydrogen molecules and halogen molecules need to be broken for the reaction to occur).

• New covalent bonds formed between hydrogen halide compound.

Describe the relative reactivity of halogens.

Reactivity of halogens decreases down the group.

How can the reactivity of halogens be worked out from displacement reactions?

The reactivity of the halogen can be worked out from whether the displacement reaction occurs:

• The more reactive element takes the place of the less reactive element. So the more reactive halogen displaces the less reactive halogen from its compound in solution.

You will know a displacement reaction has occurred with a colour change.

How are displacement reactions examples of redox reactions?

Element loses electron to give to other element (oxidation) and other element gains electron (reduction). The metal loses the electron and the non-metal gains the electron.

Explain the order of reactivity of halogens (using electronic configurations).

As the atomic size increases (going down the group and gaining electron shells) the outer electrons get further from the nucleus, so it gets harder to gain an electron. Being further away, there is less attraction between nucleus and electrons coming in so halogens are less likely to form ions - and become less reactive down the group.

Why are noble gases chemically inert (refer to electronic configuration)?

They are un-reactive elements because their atoms have stable electronic configurations (complete outer shells so there is no need to gain or lose electrons so not reactive).

List the chemical and physical properties of noble gases.

• Low density.

• Colourless.

• Low melting and boiling points.

• Poor conductors of heat and electricity.

• Density, boiling + melting points increase down the group.

• Very un-reactive elements.

• Exist as single atoms (monatomic).

• Small amounts of noble gases in our atmosphere.

Describe the uses of noble gases.

Krypton = Photography lighting (white light when electricity passed through).

Argon = Space above wine barrels to stop oxygen reacting with the wine - denser than air).

Helium = Airships/weather balloons, low-density + non-flammable.

Neon = Red/orange light when electricity passes through - illuminated signs.