Year 8 Science — 8.2 Periodic Table & Atomic Structure Term 2

Complete recall deck for Year 8 Science Unit 8.2 (Term 2) — covers matter classification, atomic structure, subatomic particles, electron configuration, the periodic table, group trends, compounds, and the history of the table. Core + Extension + Supplementary sections.

Matter

Anything that has mass and occupies volume (takes up space).

Pure substance

A substance that contains only one type of particle throughout.

Mixture

Two or more different particles physically combined but not chemically bonded, so they can be separated by physical methods.

Element

A pure substance made of only one type of atom; cannot be broken down into anything simpler.

Compound

A pure substance made of two or more different types of atoms chemically bonded (joined) in fixed proportions.

Atom

The smallest unit of an element that still keeps the unique properties of that element.

Two types of pure substances

Elements and compounds.

How is water both a pure substance and a compound?

Pure because it has only one type of particle (H2O molecules); a compound because each particle is made of different atoms (hydrogen and oxygen) chemically bonded.

Property (chemistry)

A characteristic that describes how a substance looks or behaves.

Chemical property

The ability of a substance to undergo a specific chemical change or reaction (e.g. reactivity with acid, flammability).

Physical property

A characteristic that can be observed or measured without changing the substance's identity (e.g. colour, density).

Two main classes elements are sorted into

Metals and non-metals, based on their chemical and physical properties.

Lustre

How well a material reflects light. Metals = shiny; non-metals = dull.

Thermal conductivity

The ability to transfer heat. Metals = good; non-metals = poor.

Electrical conductivity

The ability to transfer electricity. Metals = good; non-metals = poor (with a few exceptions).

Malleability

The ability to change shape under force without breaking. Metals = malleable; non-metals = brittle.

Ductility

The ability to be stretched into a wire. Metals = ductile; non-metals = not ductile.

Sonority

Whether a material rings when struck. Metals = sonorous; non-metals = not sonorous.

Density (metals vs non-metals)

Metals generally high; non-metals generally low.

Physical state at room temperature (metals vs non-metals)

Metals are solid (one exception: mercury, a liquid); non-metals are variable (solid, liquid or gas).

Boiling/melting temperature (metals vs non-metals)

Metals generally high; non-metals generally low.

The one metal that is liquid at room temperature

Mercury (Hg).

Brittle

Breaks or shatters when force is applied (typical of non-metals).

Three subatomic particles

Protons, neutrons and electrons.

Proton

Subatomic particle in the nucleus; symbol p+; relative charge 1+; relative mass 1.

Neutron

Subatomic particle in the nucleus; symbol n0; relative charge 0; relative mass 1.

Electron

Subatomic particle in shells around the nucleus; symbol e-; relative charge 1-; mass negligible (about 1/2000).

What determines which element an atom is?

The number of protons in its nucleus (e.g. 26 protons = always iron; 79 protons = always gold).

Atomic number

The number of protons in an atom.

Mass number

The number of protons plus the number of neutrons in an atom.

Neutral atom rule

A neutral atom has equal numbers of protons and electrons, so positive and negative charges cancel out.

Chemical symbol

A unique one- or two-letter code given to each element (e.g. Cl for chlorine).

Number of protons (how to find)

= atomic number.

Number of electrons in a neutral atom (how to find)

= atomic number (equals the number of protons).

Number of neutrons (how to find)

= mass number - atomic number.

How to get mass number from the periodic table

Round the atomic (average) mass to the nearest whole number.

Scale of an atom

About 500,000 carbon atoms could fit across the width of a single human hair.

Two lightest / most abundant elements in the universe

Hydrogen and helium (over 98% of all atoms).

Where heavy elements are made

At the end of a large star's life cycle, in a massive explosion called a supernova.

Charge and location of each subatomic particle

Protons: positive (+), in the nucleus. Neutrons: neutral, in the nucleus. Electrons: negative (-), in shells around the nucleus.

Sodium-23 subatomic particles

11 protons, 11 electrons, 12 neutrons (23 - 11 = 12).

Number of known elements

118.

Naturally occurring vs synthetic elements

94 occur naturally; the remaining 24 are synthetic (made in laboratories).

How elements are ordered on the periodic table

By increasing atomic number, from hydrogen (1) to oganesson (118).

First element

Hydrogen (atomic number 1).

Element number 118

Oganesson (the last element).

Who proposed the planetary atomic model, and when?

Niels Bohr, a Danish physicist, in 1913.

Bohr model - nucleus

A small, dense centre of the atom.

Bohr model - shells

Fixed circular paths (orbits) for electrons, each at a set distance representing a different energy level.

Why is it called the 'planetary' model?

It resembles the solar system: nucleus = Sun, electrons = planets, shells = planetary orbits.

When were protons and neutrons discovered relative to Bohr's model?

After it: protons in 1917, neutrons in 1932.

Steps to draw the planetary atomic model

1) Find numbers of protons, neutrons, electrons; 2) draw protons + neutrons in the centre, label the nucleus; 3) draw electron shells (circles); 4) add electrons by the configuration rule; 5) always include a key.

Electron configuration

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

Electron filling rule

Electrons fill the shell closest to the nucleus first; when it is full, they fill the next shell.

Maximum electrons in Shell 1

2.

Maximum electrons in Shell 2

8.

Maximum electrons in Shell 3 (first 18 elements)

8.

Electron configuration of helium (2)

2.

Electron configuration of fluorine (9)

2, 7.

Electron configuration of sodium (11)

2, 8, 1.

Electron configuration of magnesium (12)

2, 8, 2.

Electron configuration of phosphorus (15)

2, 8, 5.

Electron configuration for 10 electrons

2, 8.

Valence shell

The outermost electron shell of an atom.

Valence electrons

The electrons in the outermost (valence) shell.

When is a valence shell full?

When it has 8 electrons (except hydrogen and helium, which have only one shell, full at 2).

Octet rule / stable octet

Atoms are most stable when their valence shell is full (8 electrons).

Why do valence electrons matter?

They are furthest from the nucleus, so are most easily removed or shared - the basis of chemical reactivity.

IUPAC

International Union of Pure and Applied Chemistry - sets the rules for naming elements and compounds.

Sources of element names

Locations (Germanium, Francium), scientists (Einsteinium, Curium), mythology (Helium-Helios, Thorium-Thor), properties (Bromine-'stench'), minerals/ores (Lithium-'stone').

Symbol rule: length

Every symbol is one or two letters.

Symbol rule: capitalisation

First letter always uppercase; second letter (if any) always lowercase.

Why some symbols don't match the English name

Many come from Latin or Greek words (e.g. iron = Fe from Latin 'ferrum').

Are CO and Co the same?

No. CO = carbon + oxygen (a compound); Co = cobalt (one element). Capitalisation changes the meaning.

Which elements' names/symbols must you memorise?

The first 20 elements plus copper, iron, gold, lead, silver, mercury, tin, tungsten and zinc.

First 20 elements in order

H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca.

Hydrogen (symbol)

Symbol H

Hydrogen (atomic number)

Atomic number 1

Helium (symbol)

Symbol He

Helium (atomic number)

Atomic number 2

Lithium (symbol)

Symbol Li

Lithium (atomic number)

Atomic number 3

Beryllium (symbol)

Symbol Be

Beryllium (atomic number)

Atomic number 4

Boron (symbol)

Symbol B

Boron (atomic number)

Atomic number 5

Carbon (symbol)

Symbol C

Carbon (atomic number)

Atomic number 6

Nitrogen (symbol)

Symbol N

Nitrogen (atomic number)

Atomic number 7

Oxygen (symbol)

Symbol O

Oxygen (atomic number)

Atomic number 8

Fluorine (symbol)

Symbol F

Fluorine (atomic number)

Atomic number 9

Neon (symbol)

Symbol Ne

Neon (atomic number)

Atomic number 10

Sodium (symbol)

Symbol Na

Sodium (atomic number)

Atomic number 11

Magnesium (symbol)

Symbol Mg

Magnesium (atomic number)

Atomic number 12