Chemistry - 2 The Periodic Table

John Dalton - periodic table

he organised elements in order of their atomic weight

John Newlands - periodic table [3]

- also organised in order of atomic weight but noticed that the properties of every eighth element were similar.
- created his 'law of octaves' table
- assumed that all elements had been found

Dmitri Mendeleev - periodic table [3]

- organised in order of atomic weight
- switched elements so that properties matched
- left gaps for undiscovered elements

The modern periodic table [2]

- ordered by atomic number (number of protons)
- has group 0 (these elements were undiscovered when Mendeleev made his)

atomic mass vs. atomic weight

atomic mass represents the mass of a single isotope or atom, while atomic weight is the weighted average of an element, taking into account all its isotopes and their abundances

What links the elements in a group?

the number of electrons in their outermost shell

What does the group number tell us?

the number of electrons in the outermost shell

Why are noble gases unreactive?

they already have a full and stable outermost shell

What happens to the boiling point as you descend group 0?

it increases

The alkali metals

- Lithium
- Sodium
- Potassium
- Rubidium
- Caesium
- Francium

The alkali metals - mnemonic

Little Nasty Kids Rub Cat Fur

Properties of alkali metals [6]:

- soft
- highly reactive (ch)
- low density
- (relatively) low melting and boiling point
- lustrous
- good thermal and electrical conductors

alkali metal + water →

metal hydroxide + hydrogen

alkali metal + oxygen →

metal oxide

alkali metal + chlorine/fluorine/bromine/iodine →

metal chloride/fluoride/bromide/iodide

Reactivity trend in group 1

reactivity increases as you descend the group

Melting and boiling point trend in group 1

melting and boiling point decreases as you descend the group

Why does reactivity increase as you descend group 1? [5]

- there is one electron in their outer shells
- as you descend, the atoms get larger
- the outermost electron is further away from the nucleus
- the electrostatic attraction between the nucleus and the electron is weaker
- the electron can be given up more easily (reaction)

How can we demonstrate the reactivity of group 1 metals?

place pieces of different alkali metals into a trough of water

The halogens

- Fluorine
- Chlorine
- Bromine
- Iodine
- Astatine

The halogens - mnemonic

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Properties of halogens [4]:

- forms coloured vapours (ch)
- toxic (ch)
- low melting points and boiling points
- poor thermal and electrical conductors

Halogens exist as ... molecules

diatomic

Diatomic molecule

consisting of two atoms combined by a covalent bond

Halogen + hydrogen →

hydrogen halide

Halide

a halogen bearing a negative charge

Hydrogen halides are ... at room temperature

gases

Hydrogen halides are ... when dissolved in water

acids

Reactivity trend in group 7

reactivity decreases as you descend the group

Melting and boiling point trend in group 7

melting and boiling point increase as you descend the group

Metal + halogen →

metal halide

some metal halides are ...

salts

What ions do halogens form?

1- ions

A more reactive halogen...

will displace a less reactive halogen from solutions of its salts

Larger atoms ... electrons more easily descending a group

lose

Larger atoms ... electrons less easily descending a group

gain

Why does reactivity change descending a group? [5]

- more shells
- further distance from outer electrons to nucleus
- shells inbetween 'screen' the outer electrons
- weaker attractive force from nucleus
- loses electrons more easily or cannot gain them as easily

The nuclear charge ... as you descend a group because the nucleus has more ...

increases, protons

What outweighs increasing nuclear charge? [2]

- distance from nucleus
- shielding effect of shells

Are the transition elements metals or non-metals?

metals

Physical properties of transition elements [7]:

- good thermal and electrical conductors
- hard and strong
- high density
- high melting and boiling points (except mercury)
- lustrous
- sonorous
- malleable and ductile

Chemical properties of transition elements [2]:

- less reactive (than alkali metals)
- form different coloured compounds

The transition elements form ... compounds

different coloured

What charge does copper have in copper (II) sulphate?

2+

What else are transition element compounds used for?

catalysts