New(9-1) AQA GCSE Chemistry Paper 1: The periodic table Complete Revision Summary

WHY REACTIVITY OF GROUP 1 INCREASES DOWN THE GROUP ?

The Reactivity of Group 1 increases down the group as the tendency to loose an electron increases down the group. – React by loosing an electron

FACTORS AFFECTING TENDENCY TO LOOSE AN ELECTRON

• To loose an electron small nuclear charge greater size of atom and greater shielding is required
• Nuclear charge – Great the size of the atom, the outer electron becomes further away from the nucleus decreasing the nuclear charge
• Shielding – More the number of inner electrons due to increases in number of shell greater will be the shielding of the outer electron from the nuclear charge
• Size of the atoms – Greater the size of the atom, the outer electron will become further away from the nucleus resulting in decreases in nuclear charge
• Down the group the atom size increases due to increase in number of electron shells. This results in the outer electron being further away from the nucleus.
• As the outer electron becomes further away from the nucleus the nuclear charge decreases. Increase in number of shells also increases the shielding and shields the outer electron from the nuclear charge.
• Therefore, the tendency of atom to loose an electron increases down the grou resulting in increase in reactivity down the group.

GROUP 7 : Halogens ( Salt Forming)

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GROUP 7 : Halogens Physical Properties

• They are non metals
• They gain an electron to form -1 ions.
• They have low melting and boiling points
• Their melting point increases down the group due to increases in intermolecular forces.
• They are found in pairs and exist as diatomic molecules (X₂)
• They are poisonous and smelly
• Their reactivity increase down the group
• Their density increases down the group.
• They are poor conductors of heat and electricity

HALOGEN REACTION X[F,Cl,Br,I]

REACTION WITH HYDROGEN

They react with hydrogen to form hydrogen halides.

X₂(s) + H₂(g)                  2HX(g)

Reactivity decreases down the group so fluorine and chlorine reacts explosively and bromine and iodine reacts at higher temperature in the presence of catalyst.

REACTION WITH METALS

They react with metals to form ionic compounds. In Ionic compounds, halogens gain one electron from the metals to form -1 ions and attain noble gas electronic configurations.

2Na(s) + Cl₂(g)                  NaCl(s)

Mg(s) + Cl₂(g)                  MgCl₂(s)

DISPLACEMENT REACTION

The more reactive halogen displaces the less reactive halogen from its salt

As the reactivity decreases down the group, the halogen at the top can take the position of the halogen at the bottom in its compounds and will displace the less reactive halogen.

Cl₂    +               2NaBr                               2NaCl + Br₂(yellow solution formed)

(more               (salt of less reactive        (chlorine being more reactive has taken the reactive)     halogen than Chlorine)     position of less reactive bromine in its

compounds)

Cl₂ +2NaF                    No reaction

F2 – can displace all halogens

Cl₂ – can displace all Halogen except Fluorine

Br₂ – can displace only Iodine

F          Cl         Br           I

decreasing reactivity

WHY REACTIVITY OF GROUP 7 DECREASES DOWN THE GROUP ?

The Reactivity of Group 7 decreases down the group as the electron affinity or tendency to gain the electron decreases down the qroup. – React by gaining electron

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FACTORS AFFECTING TENDENCY TO GAIN AN ELECTRON

• To gain an electron, smaller nuclear charge smaller size and less shielding is required
• Nuclear Charge – Smaller the size of the atom, greater will be the force of the nucleus as the electron will be closer to the nucleus.
• Shielding – Less electrons and shells, smaller will *be the shielding which will in turn increa the nuclear charge.
• Size of Atom – Greater the size of the atom, the outer electron will become further away from th nucleus resulting in decreases in nuclear charge
• Down the group the atom size increases due to increase in number of electron shells. As a result the nuclear charge decreases.
• The size of the atom also increases down the group which makes the nuclear charge weaker
• The electron shells also increases which decreases the effective nuclear charge on the incoming electron.
• Due to all these factors, the nuclear charge decreases which decreases the tendency of gaining electrons down the group of halogen making them less reactive.

COMPARISON BETWEEN GROUP 1 and GROUP 7

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TRANSITION METALS

• Found between group 2 and group 3
• They are hard
• They are strong
• They are malleable and ductile
• They have higher densities than group 1 and group 2 hence they are used in construction purpose like iron.
• They show variable oxidation states
• They are used commercially as catalyst
• They form coloured compounds.
• They show the reaction with oxygen, water and halogen like group 1 but they react much slowly than alkali metals.

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BASIC TERMS OF PERIODIC TABLE

Periodic Table – A table that shows arrangement of all the known elements in the order of increasing atomic number. The table is organised into periods and groups.

Metals- Elements found to the left of the periodic table which are soft, shinny, conductors malleable and ductile eg Group 1; group 2 and group 3 elements

Non Metals — Elements found to the right of the periodic table which are dull, insulators Group 4,516 and 7 are non metals.

Halogens Group 7 elements are halogens as they are salt forming.

Alkali Metals Group 1 elements which react with water to form alkali

Noble Gases — Group 0 elements which are stable and do not react as they have complete outer shell

Elements found between group 2 and group 3 which have high densities, show variable oxidation states

Transition Metals and form coloured compounds

Periods- Horizontal rows of the periodic table

Groups – Vertical columns of the periodic table

Group Number – Indicates the number of electrons in the outermost shell.

Alkali Bases that are soluble in water

Displacement Reaction — When a more reactive element displaces the less reactive element from its salt

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Q1 Look at the periodic table and give two examples of each

Metal — Li, Na

Non Metal – O₂, F₂

Alkali Metal – K, Li

Halogens – F, Cl

Noble Gas – He, Ar

Semi metal or metalloid – Si

Metals that form +1 ions – Li, K

Non metal that form -1 ions – F, Cl

Metal that form +2 ions – Mg, Ca

Transition metal – Fe, Cu

Q2 Write the name of most reactive halogen and most reactive alkali metals

Halogen –F Alkali Metal – Fr

Q3 Why the alkali metals gets more reactive down the group

Down the group the atom size increases due to increase in number of electron shells. This results in the outer electron being further away from the nucleus. As the outer electron becomes further away from the nucleus the nuclear charge decreases. Increase in number of shells also increases the shielding and shields the outer electron from the nuclear charge. Therefore, the tendency of atom to loose an electron increases down the group resulting in increase in reactivity down the group.

Q4 Why halogens get less reactive down the group

Down the group the atom size increases due to increase in number of electron shells. As a result the nuclear charge decreases. The size of the atom also increases down the group which makes the nuclear charge weaker. The electron shells also increases which decreases the effective nuclear charge on the incoming electron. Due to all these factors, the nuclear charge decreases which decreeases the tendency of gaining electrons down the group of halogen making them less reactive.

Q5 Write the balanced chemical equation with state symbols of

1. a) Potassium with water

2K(s) + 2H₂O(g)                    2KOH(aq) +H₂(g)

1. b) Lithium with oxygen

4Li(s) + O₂(g)                    2Li₂O (s)

1. c) Sodium with bromine

2Na(s) + Br₂(l)                    2NaBr (s)

1. d) Chlorine with hydrogen

Cl₂ (s) + H₂(g)                    2HCl (g)

Q6 Explain displacement reaction of halogens with examples.

F₂ + 2NaCl                   2NaF + Cl₂

Cl₂ +2NaF                   No reaction

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I have tried my level best to cover the maximum of your specification. But this is not the alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.

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