atomic structure

periodic table

what does constant mean

the same

what is a chemical reaction

a reaction between 2 or more chemicals

what is a chemical change

when chemical bonds break and reform, changing the substances properties

what does conservatuion of mass mean

the total mass in a closed system remains constant overtime

what is a compound

more than one element bonded together

define law of definite proportions

a given chemical compound will always contain its original elements in a fixed and invariant proportion by mass This law states that regardless of the source or amount of a compound, the ratio of the masses of its constituent elements remains constant.

what is the law of multiple proportions

when two elements A and B form two different compounds, the masses of element B that combine with a fixed mass of element A can be expressed as a ratio of small whole numbers

what is the mass number

number of protons + neutrons

• always the bigger number and will usually contain a decimal point on the periodic table

what is the atomic number

number of protons and electrons

• not added together, but they will always be the same

how do you work out relative atomic mass (Ar)

mass number / 1/12 of 12carbon (1)

how do you work out relative molecular mass

add all the atomic masses together

what is the equation to work out mols

mass/molecular mass

define electronegativity

the ability of an atom to attract the pair of electrons in a covalent bond

describe the basic trend of electronegativity

• as you move left to right in a period, electronegativity increases

  • as you move from bottom to top in a column, electronegativity increases

what 3 factors does electronegativity depend on

1. size of positive charge on the nucleus

2. atomic radius

3. shielding of the nucleus by inner shell electrons

what is ionisation

when an atom/molecule loses or gains an electron, forming an ion

what is an ionic bond

when an atom transfers electrons to another they are attracted by electrostatic forces

what is an exothermic reaction

one that releases energy

what is an endothermic reaction

when heat or thermal energy is absorbed w

what is electron affinity

the energy change associated with an atom gaining an electron

what is the most exothermic group on the periodic table

group 7

what is electron ionisation

the energy needed to remove an electron

why is electron ionisation hard?

high fragmentation

what is electron ionisation measured in

KJ mol-1

what is the common trends in electron ionisation

energy increases across a period and decreases down a group