OCR Gateway GCSE Chemistry: C1 and C2.2: Particles and Bonding

Element

Simplest type of substance

Where all elements are found

Periodic table

Atom

Smallest part of an element / that make up a substance that still has its chemical properties

Molecule

Particle made from multiple atoms joined together by chemical bonds

Bond

Attractive force holding atoms together in a molecule

Atomic radius

Distance from centre of an atom to outside

Bond length

Distance between centres of two joined atoms

Subatomic particles

Very small particles found inside an atom

Proton

Subatomic particle with relative mass 1 and charge + 1

Neutron

Subatomic particle with relative mass 1 and charge 0

Electron

Subatomic particle with relative mass 1 / 2000 and charge - 1

Nucleus

Centre of an atom containing protons and neutrons

Shells

Rings around the nucleus of an atom in which electrons are found

Why when you add water to orange squash, the orange colour spreads out

The two substance are made from tiny particles that can mix together

Matter

What everything is made from, including particles

What particles refer to

Atoms, ions and molecules

Solid state

Regular arrangement of particles, which are very close together and vibrate around fixed positions

Liquid state, practice drawing!

Random arrangement of particles, which are close together and move around each other

Gas state

Random arrangement of particles, which are far apart and move quickly in all directions

Particle model

Explains why some properties of a substance depend on its state

Why you cannot squash a liquid or solid, using the particle model

No space for particles to move into

Why a solid has a fixed shape and cannot flow, using the particle model

Particles vibrate around fixed positions and cannot move from place to place

Compromises that are made when drawing a 3D object on paper

You can only see parts of particles facing you and some are hidden

Type of 3D diagram on paper

Isometric

Physical change

Happens when a substance changes shape or state, or breaks into pieces, and where no new substances are made

Two examples of physical changes

Melting butter and cracking eggs

Three examples of reversable physical changes

Freezing juice to make an ice lolly, mixing sand with water and dissolving sugar in water

Chemical change

When new substances are made, the properties of which can be very different from those of the original substance

Two things you may observe during a chemical change

Colour change and / or gas given off, bubbles

Three examples of chemical changes

Cooking eggs or other food, steel rusting and an acid reacting with an alkali to make a salt and water

Smallest atom

Helium

Diameter of helium atom

62 pm or 62 * 10 ^ - 12 m

Distance between two helium atoms in relation to diameter

≈ 55 x larger, making it difficult to draw gas particles to scale

Forces between particles

Forces of attraction between positive and negative charges, so electrostatic

The further apart particles are, forces become -

Weaker

What forces between particles are strongest in

Solids

What forces between particles are weakest in

Gases

Limitations of the particle model

Does not take into account forces between particles, size of particles and space between particles

Why the volume of a substance generally increases a little when it melts

Forces of attraction get weaker and particles move around each other

What atomic radii and bonds lengths are usually around

10 ^ - 10 m

What 'atom' is Greek for

Indivisible

John Dalton's contribution, 1803

Proposed all matter consists of indivisible tiny particles, atoms. Atoms of each element are different to one another because they have different masses and atoms combined in simple whole number ratios

Joseph John Thompson's contribution, 1897

Proposed a model where atoms were positively charged spheres with negatively charged electrons embedded within. Discovered electrons in his experiments of electric discharge in a high-vacuum cathode-ray tube

Plum-pudding model, devised by J.J. Thompson

Showing atomic structure, this theory held that the negatively charged electrons in an atom were floating - sometimes moving - in a sea of positive charge - the electrons being akin to plums in a bowl of pudding

Ernest Rutherford's contribution, 1911

Famous experiment where most radioactive alpha particles that were fired at a thin sheet of gold passed straight through proved that atoms were mostly empty space, with a small, dense nucleus containing positive protons - negatively charged electrons orbited the nucleus. The change he suggested in 1911 showed a rapid change of ideas about the atom which had previously been based on Thompson's model

Who, when and where Ernest Rutherford's experiment was carried out by

Geiger and Marsden under the direction of Rutherford, at Manchester University in 1909

Niels Bohr's contribution, 1922

Suggested that electrons orbited the nucleus at different energy levels - in shells. Only electrons with a specific amount of energy could be found in each shell

Chemical symbol for an atom

Write some down!

Atomic # (smallest #)

# protons in nucleus, also # electrons in an atom

Mass # (largest #)

Total # of protons and neutrons in nucleus

Isotopes of an element

Atoms with same # of protons and electrons, but different # of neutrons

What an isotope means for a chemical symbol

Same atomic #, but different mass #

All three isotopes of hydrogen

H{1, 1} / hydrogen-1, deuterium / heavy water is H{1, 2} / hydrogen-2 and tritium is H{1, 3} / hydrogen-3 (curly-bracket chemical notation is mine)

Periodic table

Chart of the elements showing the repeating pattern of their properties

What electrons do

Orbit the nucleus in shells

First shell holds a maximum of -

2 electrons

Second shell holds a maximum of -

8 electrons

Third shell holds a maximum of -

8 electrons

What the group # shows (periodic table)

# outer electrons

What the period # shows (periodic table)

# electron shells

Properties of noble gases

Inert and stable

Ion

Electrically charged particle formed when an atom, or group of atoms, loses or gains electrons

Metal atoms do what to form + ions

Lose electrons

Non-metal atoms do what to form - ions

Gain electrons

What stay constant when an atom forms an ion

# protons and neutrons

What you need to work out an ion's electronic structure

Electronic structure of the original ion, and the # electrons it lost or gained

Electronic structure of a sodium atom

2.8.1

Stable atoms or ions have -

Full outer shells

Electron diagram

Represents the electronic structure of an atom or ion

How you draw an electron diagram

A circle to represent each shell, and dots or crosses to represent its electrons. Ions go inside brackets with the change written at the top right. The element's symbol potentially written at the centres instead of showing a nucleus. Have a go at a few

Dot-and-cross diagrams

Use of both dots and crosses allow you to see which atoms provided particular electrons

What dot-and-cross diagrams can be used to show

Covalent bonds

What happens when a metal and non-metal react

Electrons are transferred from the metal atoms to non-metal atoms so both achieve more stable electronic structures

What ionic compounds contain in their solid state

Positive and negative ions arranged in a regular way, called a giant ionic lattice

Ionic bonds

Strong, electrostatic forces of attraction between metal and non-metal atoms, holding oppositely-charged ions in place, acting in all directions

Space-filling model

Way of representing ionic compounds

Binary ionic compound

Composed of two elements (a single metal e.g. sodium and non-metal e.g. chlorine)

Giant ionic lattice

Exists in three dimensions, but you can only draw it in two dimensions

What balls and sticks represent in a ball-and-stick model

Balls represent ions and plastic links represent an ionic bonds

Positive things about ball-and-stick models

Give you a clearer idea of the structure and shape of the lattice

Limitations of ball-and-stick models

Ions should be close together - bonds are forces rather than physical objects made from matter

What you can write before brackets in ions notation

Coefficient

What we need to know to find formulae of ionic compounds

Charges of ions

How we can find charges of ions

Periodic table

Transition metals form -

More than one ion

Positive (group) ions

Ammonium, NH4+

Negative (group) ions

Hydroxide, OH -, nitrate, NO3 -, sulfate, SO4 2- and carbonate, CO3 2-

Covalent bond

Shared pair of electrons, forming between two non-metal atoms when they get close enough to share atoms in their outer shells. They therefore complete their outer shells

What each pair of electrons in the intersection of overlapping circles of a dot-and-cross diagram represents

A covalent bond

When drawing a dot-and-cross diagram for covalent bonds, only the what are shown?

Outer shells

Stick notation

Each line between symbols represents a bond. You can have multiple lines to represent multiple e.g. double bonds

Molecule

Particle in which non-metal atoms are joined to each other by covalent bonds

Simple molecule

Only contains a few atoms

Examples of simple molecules

Hydrogen, oxygen, water and carbon dioxide

Covalent bonds between atoms in a simple molecule are -

Strong

Intermolecular forces in a simple molecule are -

Weak

Intermolecular forces

Between molecules

Limitations of ball-and-stick models (for simple molecules)

Sizes of atoms and lengths of bonds are exaggerated, and it suggests that electrons that make bonds do not move

Displayed formula

Drawn for simple molecules, where each atom is represented by its chemical symbol and each covalent bond is a straight line

Limitations of a displayed formula

Does not show three-dimensional shape of molecule