Chapter 4: Chemical bonding

Question 1

What is chemical bonding?

Answer 1

• Chemical bonding occurs due to the transfer/sharing of electrons between atoms in order to achieve the electronic configuration of a noble gas.

Question 2

Why do noble gas have stable electronic configurations?

Answer 2

• This is because of their completely filled electron shells.
• E.g. Helium
  Electronic configuation: 2
• E.g. Neon
  Electronic configuration: 2,8
• E.g. Argon:
  Electronic configuration: 2,8,8

Question 3

What is a noble gas configuration?

Answer 3

• A noble gas configuration is made out of 2 electrons in the first electron shell, followed by 8 electrons each in the second and third electron shells.
• E.g. Helium; which has one completely filled electron shell, has a DUPLET electronic configuration.
• E.g. Neon and argon; which has 2 and 3 completely filled electron shells respectively, have an OCTET electronic configuration.

Question 4

What happens when there is a stable configuration?

Answer 4

• Due to their stable configurations, noble gases do not form chemical bonds and they usually exist as a single atom or are MONATOMIC.

Question 5

How do we achieve a completely filled valence/outermost shell of electrons?

Answer 5

• The atoms of all other elements in the periodic table lose/gain/share electrons.

Question 6

Where are metals mainly found in the periodic table?

Answer 6

• Metals are mainly found in groups 1-3 of the periodic table.

Question 7

What happens when atoms of METALS have less than 4
valence /outermost electrons?

Answer 7

• As atoms of metals have less than 4 valence/outermost electrons, they tend to lose electrons, which are transferred to atoms of non-metals.

Question 8

Where are non-metals mainly found in the periodic table?

Answer 8

• Non-metals are mainly found in groups 14-17 of the periodic table.

Question 9

What happens when atoms of NON-METALS have less than 4
valence /outermost electrons?

Answer 9

• As atoms of non-metals usually have 4 or more than 4 valence electrons, they tend to gain electrons from atoms of metals/share electrons with atoms of other non-metals.

Question 10

How are ions formed?

Answer 10

• Ions are formed when atoms gain or lose electrons.

Question 11

How are anions formed?

Answer 11

• Anions are formed when non-metals gain electrons.

Question 12

How are cations formed?

Answer 12

• Cations are formed when metals lose electrons.
• E.g. A magnesium atom loses 2 electrons to form a magnesium ion, and an oxygen atom gains 2 electrons to form an oxygen (O2) ion.

Question 13

skip this card.

Answer 13

SEE MAGNESIUM AND OXYGEN’S gain/loss of electrons and noble gas electronic configuration IN NOTEBOOK!

Question 14

What are ionic bonds?

Answer 14

• Ionic bonds refer to the electrostatic attraction between cations and anions.
• Thus, an ionic compound is formed.
• E.g. Magnesium reacts with oxygen to form the ionic compound, and magnesium oxide and magnesium oxide can be represented using a DOT-and CROSS diagram.

Question 15

Are ionic compounds neutral? How does it benefit the/its compound?

Answer 15

• Ionic compounds are electrically NEUTRAL, so this means that the total charge of the cations cancels out the total charge of the anions.
• Thus, the ratio of the cations and anions required to form an ionic compound can be determined/estimated.

Question 16

What are polyatomic ions?

Answer 16

• Polyatomic ions are ions that are made up of 2 or more atoms covalently bonded together.
• E.g. The ammonium ion (NH4+) and the sulfate ion (SO4 2-)

**A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms

Question 17

What is a giant ionic crystal lattice?

Answer 17

• A giant ionic crystal lattice is where, an ionic compound in the solid state that has oppositely charged ions, is arranged REGULARLY.
• In the ionic compound sodium chloride (NaCl):
• the Na+ ions and cl ions are arranged alternately to prevent the repulsion in a 3-dimensional structure.
• Each cation is surrounded by 6 anions and vice versa
• Strong electrostatic forces of attraction exist between the oppositely charged ions, thus holding the structure together.

Question 18

How do atoms achieve the noble gas configuration?

Answer 18

-Atoms share electrons to achieve the noble gas configuration.

Question 19

How is a covalent bond formed?

Answer 19

• A covalent bond is formed when 2 electrons are shared between the 2 atoms.
• Thus, 2 covalent bonds are formed when 4 electrons are shared between 2 atoms, etc.
• E.g. A hydrogen atom has 1 valence electron, and it shares 1 electron with another hydrogen atom to achieve an outermost shell completely filled with 2 valence electrons. Thus, a single covalent bond is formed between the 2 HYDROGEN atoms.
  ** A single covalent bond is made up of 2 electrons.
• E.g. an oxygen atom has 6 valence electrons, and it shares 2 electrons with another oxygen atom to achieve an outermost shell completely filled with 8 valence electrons. Thus, a double covalent bond is formed between the 2 OXYGEN atoms.
  ** A double covalent bond is made up of 4 electrons.

Question 20

How are diatomic molecules formed?

Answer 20

• Diatomic molecules are formed when 2 atoms are covalently bonded together.
• E.g. Hydrogen (H2), nitrogen (N2), oxygen (O2), and chlorine (Cl2).

Question 21

What are the 2 different scenarios that covalent bonding ca occur between?

Answer 21

1. Atoms of the same element form molecules of the element.
   (E.g. H2, N2, O2)
2. Atoms of different elements form molecules of a compound.
   (E.g. H2O, CO2, NH3)

Example 1:
* A water molecule (H2O) molecule consists of 2 hydrogen atoms and 1 atom covalently bonded together. *
- A hydrogen atom has 1 valence electron, and it requires 1 more electron to achieve 1 noble gas electronic configuration.
- An oxygen atom has 6 valence electrons, and it requires 2 or more electrons to achieve a noble gas electronic configuration.
- 2 hydrogen atoms each share 1 electron with an oxygen atom to achieve a noble gas electronic configuration.

Question 22

What happens when a molecule consists of 3 or more atoms?

Answer 22

• If a molecule consists of 3 or more atoms, the atom that forms the most number of bonds will be the central atom in the molecule.
• E.g. In a water molecule, the oxygen atom forms 2 covalent bonds with the hydrogen atoms, while each hydrogen atom forms 1 covalent bond with the oxygen atom. Thus, oxygen is the central atom in the water molecule.

Question 23

How are atoms of metals and cation arranged?

Answer 23

• Atoms of metals lose electrons to form cations.
• The cations are arranged in an orderly manner and are surrounded by a “sea of delocalised electrons” (are free to move in the lattice) in a giant metallic lattice.

Question 24

What are metallic bonds?

Answer 24

• Metallic bonds are the strong electrostatic forces of attraction that exist between cations and the “sea of delocalised electrons”.
  Example:
• Sodium loses its valence electron to achieve a stable electronic configuration. *
• The electron that is lost is NO longer in the metal atom, it is mobile, and it moves around in the metallic lattice, and this is known as delocalisation.
• There are strong electrostatic forces of attraction between the sodium ions, and the delocalised electrons in the giant metallic lattice.

Question 25

What is delocalisation?

Answer 25

• Delocalisation is the process when the electron that is lost is NO longer in the metal atom, it is mobile, and it moves around in the metallic lattice.