1.6 The Periodic table

Differences of Mendeleev’s periodic table

• arranged elements by increasing atomic weight, modern uses atomic number

• left gaps for undiscovered elements and predicted their properties, modern includes all known elements

• did not include noble gases

• contains significantly less elements

• altered order to group elements with similar observed properties

• has no blocks of lanthanides and actinides, which are present today

Periodic table

organised list of all known elements arranged by atomic number

Element

substance that consists of only one type of atom and cannot be broken down into anything simpler by chemical means

Structure of periodic table

made up of groups (vertical columns) and periods (horizontal rows)

Position of metals in periodic table

separated by ‘stepped line’ running below boron to astatine

Properties of metals

• good conductor of electricity and heat

• generally high melting points

• ductile and malleable

• sonorous (makes a ringing sound when struck)

• all solids other than mercury

Properties of non-metals

• poor conductor of electricity

• generally low melting points

• brittle (breaks when hammered)

• not sonorous

• mostly gases other than solids C, P, S, Se, I and liquid Br

Names of groups in periodic table

1- Alkali metals

2- Alkaline earth metals

7- Halogens

0- Noble gases

Why elements with similar properties appear in the same group

have the same number of electrons in their outer shells which they must gain or lose to form a positive or negative ion with stable electronic configuration

Properties of alkali metals

• low density, first 3 floating in water

• very soft and easily cut with a knife

• shiny when cut but tarnish rapidly in air

• low melting points, decreasing down the group

• conduct electricity

Colour of alkali metals

white compounds and colourless solutions

Alkali metals in water equation

alkali metal + water→ alkali metal hydroxide + hydrogen

Observations of lithium in water

• floats on surface of water

• moves about on surface

• fizzing

• heat is released

• metal disappears

• colourless solution formed

Observations of sodium in water

• same observations as lithium

• metal melts into silvery ball

• sometimes orange flame produced

Observations of potassium in water

• same observations as lithium

• rapidly metal melts into silvery ball

• lilac flame produced

• small explosion/ crackling noise

Safety precautions with alkali metals

• Use tweezers when lifting

• Safety screen and wear safety glasses

• Small piece of metal

• Large volume of water (trough)

• store under oil to prevent reaction with oxygen/ moisture

Why do alkali metals so vigourously

all have one electron in outer shell which is easy to lose

Pattern of reactivity in alkali metals

reactivity increases going down group

Why reactivity increases

atomic radius increases causing nuclear attraction to decrease so it’s easier to lose an electron, and shielding from electrons between shells

Properties of halogens

• diatomic, linked by single covalent bond

• toxic so use fume cupboard when storing

• very reactive

• do not conduct electricity

Fluorine

yellow gas

Chrloine

yellow-green gas, colourless solution

Bromine

red-brown liquid, orange solution

Iodine

grey-black solid, brown solution

Pattern of state in halogens

darker in colour and change from gas to liquid to solid

Reason for state changes in halogens

melting point increases going down group

Pattern of reactivity in halogens

reactivity decreases going down

Why reactivity decreases

atomic radius decreases causing nuclear attraction to increase so it’s harder to gain an electron, and shielding from electrons between shells

Sublimation

change of state from solid directly to gas on heating, without passing through the liquid phase

Iodine sublimation

turns from grey-black solid to purple gas

Test for chlorine gas

damp universal indicator paper turn red, then bleaches white if present

Displacement

more reactive element displaces (pushes out) less reactive from compound,

Colours of halogen displacement reactions

starts off with colourless solution and result reflects halogen that’s been pushes out

Properties of noble gases

• inert (unreactive)

• colourless gases

• low boiling points

• boiling point increases going down group

Why are noble gases unreactive

stable electronic configurations as they have full outer shell

Why boiling points of noble gases decrease

forces of attraction between smaller atoms is very weak so the bigger the atom the stronger the force

Properties of transition metals

• High melting point (except mercury)

• High density

• Low reactivity with water

• React to form ions with different charges

• Form coloured compounds

Colour of copper(II) oxide

black solid

Colour of copper(II) carbonate

green solid

Colour of hydrated copper(II) sulfate

blue crystals

Colour of any copper(II) salt in solution

blue solution