topic 6 - groups in the periodic table

explain why some elements can be classified as alkali metals

• they form alkaline solutions

• when they react with water

what group in the periodic table are alkali metals

group 1

explain why some elements can be classified as halogens

• they form salts

• when they react with metals

what group in the periodic table are halogens

group 7

explain why some elements can be classified as noble gases

they’re all unreactive, non-metal gases

state the physical properties of alkali metals

• soft

• relatively low melting points

state word reaction of lithium with water

lithium + water → lithium hydroxide + hydrogen

state word reaction of sodium with water

sodium + water → sodium hydroxide + hydrogen

state word reaction of potassium with water

potassium + water + potassium hydroxide + hydrogen

describe pattern of reactivity of alkali metals with water

• all alkali metals react vigorously with cold water

• all reactions give off hydrogen gas

• and produce metal hydroxide

• speed and violence of reaction increases

• as you go down group 1

• demonstrating that reactivity increases as you go down group 1

state key safety points when reacting alkali metals with water

• use plastic safety screen

• use small pieces of metal

• use large volume of water

• use tweezers to hold metal

• wear thick rubber gloves

explain the pattern in the reactivity of alkali metals with water based on electronic configuration

• reactivity increases as you go down group 1

• as the atoms get bigger

• distance of outermost electron shell from the nucleus increases

• attraction between nucleus and outermost electron shell weakens

• meaning electrons are lost easier

state colour of chlorine at room temperature

pale green

state physical state of chlorine at room temperature

gas

state colour of bromine at room temperature

brown

state physical state of bromine at room temperature

liquid

state colour of iodine at room temperature

purple-black

state physical state of iodine at room temperature

solid

describe the pattern in physical properties of halogens

• melting and boiling points increases

• as you go down group 7

explain the pattern in physical properties of halogens

• as you go down group 7

• molecules become larger

• intermolecular forces become stronger

• thus more energy is needed to overcome these forces

describe chemical test for chlorine

• gently heat the unknown substance in a test tube

• hold damp blue litmus paper in the gas given off

• chlorine gas will cause the litmus paper to turn red then bleached

describe reaction of halogens with metals

• halogens react with some metals

• to form ionic compounds

• which are metal halide salts

recall what halogens produce

hydrogen halides

state what happens when hydrogen halides dissolve in water

form acidic solutions

describe the relative reactivity of chlorine

• chlorine will displace iodine and bromine

• in displacement reactions

• as reactivity decreases as you go down group 7

describe the relative reactivity of bromine

• bromine will displace iodine

• and be displaced by chlorine

• in displacement reactions

• as reactivity decreases as you go down group 7

describe the relative reactivity of iodine

• iodine will be displaced by chlorine and bromine

• in displacement reactions

• as reactivity decreases as you go down group 7

explain why the displacement reactions of halogens are redox

• both oxidation and reduction occur in the reaction

• with the more reactive halogen acting as the oxidising agent

• and thus being reduced

• and the less reactive halogen acting as the reducing agent

• and thus being oxidised

oxidation definition

loss of electrons

reduction definition

gain of electrons

explain why noble gases are chemically inert compared to other elements

• other elements participate in reactions to complete their outer shell

• by losing, gaining or sharing electrons

• noble gases have full outer shells

• making them unreactive and inert

state properties of noble gases

• low density

• non-flammable

• chemically inert

• low melting/boiling point

explain how the use of noble gases in balloons depends on their properties

• helium is used for filling balloons

• as it is less dense than air

• and non-flammable

explain how the use of noble gases in lighting depends on their properties

• neon and argon are used for lighting

• as they emit a bright glow

• when electric current passes through them

• with their inert nature preventing reactions

• that could affect light output

explain how the use of noble gases for welding depends on their properties

• argon is used for welding

• as its inert nature protects the weld area

• from atmospheric gases (oxygen and nitrogen)

• which could cause defects in the weld

explain how the use of noble gases in low energy light bulbs depends on their properties

• argon is used in low energy light bulbs

• as it glows brightly

• when a high potential difference is applied

• to the argon gas under low pressure

describe the pattern in the physical properties of noble gases

• noble gases have low melting/boiling points

• boiling/melting point increases as you go down group 0

explain the pattern in the physical properties of noble gases

• as you go down group 0, relative atomic mass increases

• causing an increase in strong forces of attraction between atoms

• increasing the amount of energy needed to overcome these forces of attraction

• causing a decrease in reactivity as you go down group 0