Periodic Table Trends 🧪

Question 1

Period and Group Numbers

Answer 1

• Periods: Rows
• Groups: Columns
• Group numbers corresponds with the number of valence electrons. Chemical properties of an element depends on the number of valence electrons as these electrons are invovled during a reaction. Therefore, elements in the same group have similar chemical properties.
• Period number corresponds to number of main electron shells.

Question 2

Different types of elements on the periodic table

Answer 2

Question 3

Electronegativity

Answer 3

Electronegativity is the attraction an atom has for its valence electrons. Metals and non-metals can be definied in terms of electronegativity.
* Metals have low electronegativities, a weak attractive force for valence electrons and non metals have high electronegativities.
* Electronegativity increases from bottom to top in groups, and increases from left to right across periods

Question 4

Explain electronegativity of metals and non metals

Answer 4

Metals are electropositive in nature because all metals lose electrons from their outermost shell in order to become stable and hence become positively charged. Therefore have a weak attractive force for valence electrons. Non-metals are electronegative in nature because all non-metals gain electrons in order to become stable and hence become negatively charged. Have a strong attraction for valence electrons.

Question 5

How is electronegativity determined

Answer 5

1. Core charge
2. Atomic radius

• Electronegativity increases across a Period because core charge increases and atomic radius decreases. Except for Group VIII because there are the same number of occupied electron shells, yet a greater number of protons in the nucleus.
• Electronegativity decreases down a Group. This is because core charge is constant and atomic radius increases.

Question 6

Core Charge

Answer 6

Core charge = charge on the nucleus - charge on inner shell electrons. The higher the core change, the stronger the attraction for valence electrons, therefore higher electronegativity.

Going down a group, core charge remains constant, equal to the group number.

Question 7

Atomic Radius

Answer 7

As atomic number increases across a period, core charge increases, therefore attraction of nucleus to valence shells increases. As a result, valence electrons are drawn close to the nucleus and atomic radius decreases. The large an atom, the greater distance between protons in the nucleus and valence electrons, therefore attraction becomes weaker and electronegativity lowers. Atomic radius of elements increases down a group, as each successive element increases by one more electron shell.

Question 8

Transition from metals to nonmetals

Answer 8

travelling across the Periodic Table there is not a sudden, discrete change from metals to non-metals. The transition from metals to non metals is gradual, and metalloids show some characteristics of both metals and non-metals.

Question 9

Metal and Nonmetal Reactivity Periodic Table Trends

Answer 9

Metallic character increases down a Group, since the valence shell electrons are easily lost as there is more distance from the attraction of the nucleus.
Metallic character decreases across a Period, since the outer shell is no further from the nucleus, yet there are more protons in the nucleus, so the electrons experience greater attraction for the nucleus and are held more tightly.

nonmetallic characteristics increases from left to right and decreases down groups. (except group VIII)

Question 10

Metal Reactivity Series

Answer 10

The reactivity of a metal is determined by its ability to form a positive ion. For example, potassium is extremely reactive because it has only one valence electron, so it is very easy to lose it forming a positive ion.
One the other hand, copper is a weakly reactive metal because it has more valence electrons so it is harder for it to become a positive ion (less reactive)

Question 11

Metal Displacement Reaction (Single)

Answer 11

A metal displacement reaction occurs when a more reactive metal is placed in an aqueous solution of ions of less reactive metal. The more reactive metal become the ions in solution and the less reactive metal ions become the solid.

a single-displacement reaction is characterized by one cation or anion trading places with another to form a new product.
Use a metal reactivity table: a metal can displace any metal lower in the activity series (cations)

Question 12

Ionic Radius

Answer 12

Question 13

Ionisation Energy

Answer 13

• Ionisation energy is a measure of the energy required to remove the outermost electron from an atom.
• Ionisation energy decreases down a Group: outer shell is further from the nucleus and electrons are held less tightly by attraction.
• Ionisation energy increases across a Period since there is an increasing number of protons in the nucleus, but the same number of occupied shells, therefore outer shell electrons are held more tightly.

Question 14

Double Displacement Reaction or Precipitation Reaction

Answer 14

• Insoluble substance is formed in a solution
• Ions of 2 compounds exchange places in an aqueous solution to form two new compounds
• Cation from one reactant combines with an anion from another reactant to form an insoluble compound that previpitates out of solution.

Question 15

Metals + Acid (SIngle displacement of a gas)

Answer 15

Question 16

Combustion

Answer 16

Describes a rapid chemical reaction with oxygen in which a substance burns to release energy in the form of heat and light. Therefore, all combustion reactions can be classified as exothermic reactions.
CH4 + 2O2 → CO2 + 2H2O
The methane (fuel) is burned in the presence of oxygen to form carbon dioxide and water

Incomplete combution occurs when there is limited oxygen, and the products are either carbon (soot) or carbon monoxide (CO) instead of carbon dioxide (CO2).

Question 17

Combination or Synthesis Reaction

Answer 17

• A chemical reaction where two reactants combine to form one product
• Two non metals react to form a molecular compound
• Metals and nonmetals react to form an ionic compound
• Where A + B 🡢 AB
• E.g. Magnesium + oxygen 🡢 magnesium oxide
• Sodium + chlorine gas 🡢 sodium chloride
• Elements react with oxygen to form oxides, metal oxides react with carbon dioxide to produce metal carbonates, react with water to produce metal hydroxides, react with sulfur dioxide to produce metal sulfites.

Question 18

Decomposition Reaction

Answer 18

A chemical reaction where one reactant breaks apart into two or more products
Where AB 🡢 A + B
H2CO3 🡢 H2O + CO2
The hydrogen carbonate is separated into water and carbon dioxide

E.g. Elephant’s toothpaste: hydrogen peroxide 🡢 water + oxygen