Chemisty Definitions - Unit 1

Element

Element

Contains only one type of atoms. They cannot be broken down into simpler substances by chemical means

Compound

two or more elements chemically combined

Radius of atom

1x10^-10m

Radius of a nucleus

1x10^-14m

Ions

Charged particle formed whenever an atom gains or loses electrons

Cations

positively charged ions

Anions

negatively charged ions

Isotopes

Atoms that have the same atomic number and different mass numbers

Diatomic

Only two atoms are covalently bonded in the molecule

Molecule

two or more atoms covalently bonded

Alloys

a mixture of two or more elements, at least one of which is a metal

Nanoparticles size

1nm/1x10^-9m

Nanoparticles

A structure that is 1 - 100nm in size and contains a few hunderd atoms

Sublimation

Change from the soild state to the gas state without going through the liquid state

Relative atomic mass

the mass of an atom compared with the mass of the carbon-12 isotope

Water of crystallisation

Water that is chemically bonded into crystal structure

Hydrated solid

one that contains water of crystallisation

anhydrous substance

one that does not contain water of crystallisation

Degree of hydration

The number of moles of water of crystallisation per mole compound

Removing water of crystallisation

Removed from a hydrated substance by heating it to constant mass

Acid

a substance that produces hydrogen ions when dissolved in water

Base

a substance that produces hydroxide ions when dissolved in water

Alkali

water soluble base

Salt

A compound that is formed whenever some or all of the hydrogen ions in an acid are replaced by metal ions

strong acid/alkali

These will completely ionise in water, will dissociate to produce a large quantity of H+ or OH- ions

weak acid/alkali

These are only partially ionised in water

Concentrated

Large number of acid/alkali particles per unit volume of solution

Dilute

Small number of acid/alkali particles per unit volume of solution

Concentration unit

mol/dm^3 (moles per decimetre cubed)

pure substance

A single element or compound, not mixed with any other substance

Formulation

Mixture of different subsatances in carefully measured quantities that has been designed as a useful product

Solute

The soild that is being dissolved

Solvent

The liquid in which the solute is dissolved

Solution

A mixture of a dissolved solute and a solvent

Satureated solution

One in which no more solute will dissolve at a certain temperature

Miscible

describes liquids that dissolve in one another in all proportions

Immiscible

Liquids that do not mix but instead separate into two layers

Solubility

The mass of solute require to saturate 100g of water at a certain temperature

Unit of solubility

g/100g

Formula of an ionic compound

The ratio of ions involved in its lowest terms

Formula of a covalent compound

The number of each type of atom present in the molecule

allotropes

Different forms of the same element that exist in the same physical state

displacement reactions of the halogens

a more reactive halogen will displace less reactive halogens form solutions containings halide ions