C2 The periodic table (Combined)

KEY terms flash card o

atomic number

The number of protons in an atom.

mass number

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

relative atomic mass

The average mass of all the different isotopes of an element in their relative proportions.

electron shell

A region of space around an atomic nucleus in which electrons are found. Also called energy levels.

electronic structure

A description of the way the electrons are arranged in a particular atom.

group

A vertical division in the periodic table. Gives the number of outer electrons in an atom.

period

A horizontal division in the periodic table. Gives the number of electron shells in an atom.

physical property

A property of a substance that does not depend on a reaction with another substance.

chemical property

A property of a substance that depends on a reaction with another substance.

alkali

A solution containing hydroxide ions that will react to neutralise an acid.

ion

An atom that has either lost electrons to become positively charged or gained electrons to become negatively charged.

alkali metal

One of the metals from Group 1 in the periodic table that react with water to produce alkali solutions.

halogen

The elements of Group 7 in the periodic table.

displacement reaction

A class of reaction in which a more reactive element displaces a less reactive one from a compound.

How were the elements in Mendeleev's periodic table sorted?

Sorted by atomic weight

Why did Mendeleev leave gaps in his periodic table?

As he thought that some elements hadn't been discovered yet

How are elements arranged in the modern periodic table?

By atomic mass and chemical properties

As the alkali metals go down the group their reactivity…

Increases

As the halogens go down the group their reactivity…

Decreases