Chemistry - Atomic Structure

Isotope

An atom that have the same atomic number but different atomic mass numbers.

Mass number

number of protons and neutrons in nucleus of an atom

Relative atomic mass

the average mass of an atom of an element

John Dalton

Introduced the atomic theory, that elements consist of small indivisible particles.

Joseph Thomson

Discovered negative particles, electrons

Ernest Rutherford

Made the nuclear model (plum pudding) , compact nucleus and negative charges surrounding the nucleus

Niels Bohr

Changed the plum pudding model into a small nucleus with orbiting electrons and specific distances from the nucleus

James Chadwick

Discovered neutron particle in the nucleus of atoms.

Antoine Lavoiser

Grouped elements based on there properties.

Johaan Wolfgang

Recognised triads of elements with chemically similar properties.

John Newland

Noticed similarities between elements which differed by atomic weights of 7, in groups of 8.

Dimitri Mendeleev

Arranged elements with similar properties and atomic weight together.

What did Dimitri Mendeleev do?

He predicted elements using his table and left gaps for them on his table.

Group 1

Alkali metals

Properties of group 1 metals

Float on water, soft and dull

How does group 1 react with oxygen?

Fizzes and hydrogen gas is evolved, burns a flame and then produces a white powder

What happens to the reactivity of the group 1 metals as you go down the group?

It gets more vigorous as you descend the group.

Explain the trend in reactivity for alkali metals?

As you descend the group, the reactivity increases, this is because the size of the atom increases as there are a greater number of shells. Therefore there is a weaker nuclear attraction because the distance the nucleus to the outer shell electron increases. Therefore the outer shell electron is lost more easily.

Group 7

Halogens, diatomic molecules.

Describe the trend in melting points as you descend group 7.

Melting points and boiling points increase as you descend. The atomic radius increases as you go down the group. The forces of attraction between the molecules are greater. The forces of attraction require more energy to overcome.

Explain the change in reactivity as you go down group 7.

The reactivity decreases as you go down the group because the atomic radius gets larger. The outer electron gets further from the nucleus as you descend the group. This reduces the force of attraction. The inner shells of electrons shield the outermost electron from the electrostatic attraction of the nucleus. Both factors make it harder to gain an electron as you descend the group.

Group 0

Noble gases, have full outer shells

Transition metal properties

Good conductors of electricity and thermal energy, strong and hard texture, high density, high melting/boiling points, used as catalysts to speed up chemical reactions.