Chemistry_ Term 2 (2023)

Matter

Matter

Anything that has mass and takes up space

Properties of matter (SCaM BoreDoMM)

Strength. Conductivity. Malleability and ductility. Brittleness. Density. Magnetism and non-magnetism. Melting and boiling points.

Mixtures

Formed when two or more substances are combined and mixed physically, without chemically bonding

Properties of mixtures

Composition can vary and consist of two or more elements or compounds. Properties are the same of those of the constituent substances. Constituents can be separated by physical methods.

Homogenous mixtures

Have the same constant composition throughout the mixture.

• substances in the mixture can no longer be distinguished from each other and the mixture looks the same throughout.

Heterogenous mixtures

Non-uniform mixture of substances, of which the particles of the substances in the mixture remain separate.

• the particles are not evenly distributed and sometimes occur in more than one state.

Pure substances

Consist of one type of substance only.

Elements

Pure substances that cannot be broken down into simpler substances by chemical methods.

Properties of elements

Consists of one kinds of atom. Properties are unique. Constituents cannot be separated by physical/chemical methods.

Compounds

Pure substances made of the atoms of elements that are chemically bonded in fixed ratios.

Properties of compounds

Composition is constant. Properties differ from those of the constituent elements. Constituents can be separated by chemical methods.

Brownian motion

The random movement of microscopic particles suspended in a liquid or gas, caused by collisions between these particles and the molecules of the liquid or gas.

Properties of a solid

Not easily compressible. Particles are bonded in a fixed position. Strong forces between the particles. Small spaces between the particles. Particles vibrate in their rest position.

Properties of a liquid

Not easily compressible. Forces between the particles weaker than in solids. Spaces between particles are slighter larger than in solids. Particles move about more vigorously. Exert pressure in all directions on all sides of the container.

Properties of a gas

Compressible. Particles are far apart. Virtually no forces between the particles. Particles move around at high speed. Exert pressure as a result of collisions of particles on objects.

Boiling point

Temperature at which the vapour pressure of a substance is equal to atmospheric pressure.

Melting point

Temperature at which the solid and liquid phases of a substance are at equilibrium.

Freezing point

The temperature at which a liquid changes into a solid by the removal of heat.

Phase changes

Solid to liquid = melting.

Liquid to solid = freezing.

Liquid to gas = evaporation.

Gas to liquid = condensation.

Solid to gas = sublimation.

Gas to solid = deposition.

Kinetic molecular theory

Matter consists of small particles. The particles are in constant motion. There are forces of attraction between the particles. Particles collide and exert pressure.

Temperature

A measure of the average kinetic energy of the particles making up a substance.

The effect of temperature on the particles in a substanc e

If a substance is heated, the particles gain more energy, move faster and their average kinetic energy increases. If the particles gain enough energy, they can overcome the intermolecular forces between them and move further apart (change phases).

Kelvin (K)

SI unit for temperature. To convert from ℃ to K, add 273,15 to the amount.

Latent heat

The energy absorbed or released during a state change.

Cation

A positively charged ion. Always named first in a compound.

Anion

A negatively charged ion. If monatomic , change the end to -ide.

Relative atomic mass

The weighted average of the mass of all the isotopes of an element.

Isotope

Atoms with the same atomic number but different mass numbers due to differing numbers of electrons.

Orbitals

Region of space around the nucleus where there is a 90% chance of finding an electron.

S-orbitals

Spherical orbitals. Only one per energy level.

P-orbitals

Dumbbell shaped. Three per energy level.

Aufbau's principle

Electrons occupy orbitals so that the atom's energy is minimized.

Hund's rule

When filling sub-levels of p-orbitals, electrons are placed in individual orbitals before they are paired up.

Pauli's Exclusion principle

Only two electrons can occupy an orbital and these electrons must spin in opposite directions.

Core electrons

Electrons that fill the inner energy level.

Valence electrons

The electrons that occupy the outermost energy level of an atom.

Valency

The number of electrons that need to be added or removed in order for an element to reach noble gas configuration.

• the number of bonds that an atom can form.

Electronegativity

A measure of how strongly the atom attracts the shared pair of electrons in a chemical bond. Is affected by the atomic number and the distance of the valence electrons from the nucleus. Increases across a period and decreases down a group.

Ionization energy

The energy required to remove the outermost electron from an element in the gaseous phase. Increases across a period - electrons are held more tightly by atoms because of the bigger positive charge in the nucleus. Decreases down a group - electrons are further away from the nucleus.

Atomic radius

Distance from the nucleus to the outermost stable electron orbital. Decreases across a period and increases down a group.

Electron affinity

The energy released when an electron is accepted by an atom or molecule in the gaseous state to form an anion. Increases across a period and decreases down a group.

Melting point, Boiling point and Density as a trend in the periodic table

All increase steadily from group 1 -14 and then suddenly drop in group 15. They then increase again from 16 - 18.

A chemical bond

A force that binds atoms together, formed when atoms are held together by attractive forces.

Octet rule

Atoms tend to form bonds so that they are surrounded by 8 electrons.

Covalent bond

Pairs of electrons are shared between atoms. Occurs when two non-metals interact. Valence electrons are distributed as shared or bond pairs and unshared or lone pairs.

Ionic bond

Electrons are transferred from one atom to another. Occurs when a metal and non-metal interact.

Metallic bond

The electrostatic attraction between positive metal ions and delocalized electrons. Occurs when two metals interact.

Metals

Solids that consist of atoms that are tightly packed together in a metallic crystal lattice. Lose control over its valence electrons.

Water of crystallization

Water molecules trapped inside ionic crystals. Absorbed through the atmosphere.