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Chemistry: Atomic Structure, Bonding, and Periodicity - Ionic, Covalent, and Metallic Bonding

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Octet Rule states that atoms tend to gain, lose, or share electrons to achieve a stable outer shell of eight electrons, similar to a noble gas (e.g., NeNe, ArAr).

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Ionic Bonding occurs between metals and non-metals via the transfer of electrons. This results in the formation of cations (Mn+M^{n+}) and anions (Xm−X^{m-}), held together by strong electrostatic forces.

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Covalent Bonding involves the sharing of electron pairs between non-metal atoms. Single bonds share 2 electrons, double bonds share 4 electrons (O=OO=O), and triple bonds share 6 electrons (N≡NN\equiv N).

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Metallic Bonding is defined as the electrostatic attraction between a lattice of positive metal ions and a 'sea' of delocalized valence electrons, which accounts for high electrical conductivity.

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Valence Electrons are the electrons in the outermost shell that participate in bonding. For example, Group 1 elements have 11 valence electron, while Group 17 elements have 77.

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Electronegativity is a measure of an atom's ability to attract a bonding pair of electrons. Large differences in electronegativity typically lead to ionic bonds.

📐Formulae

2n2 (Maximum electrons per shell n)2n^{2} \text{ (Maximum electrons per shell } n\text{)}

Ionic Compound Neutrality: n(Cationx+)+m(Aniony−)=0\text{Ionic Compound Neutrality: } n(Cation^{x+}) + m(Anion^{y-}) = 0

Formal Charge=V−L−12S\text{Formal Charge} = V - L - \frac{1}{2}S

ZAX (Atomic notation where A=mass number and Z=atomic number)_{Z}^{A}X \text{ (Atomic notation where } A = \text{mass number and } Z = \text{atomic number)}

💡Examples

Problem 1:

Determine the chemical formula for the ionic compound formed between Aluminum (AlAl, Group 13) and Oxygen (OO, Group 16).

Solution:

The formula is Al2O3Al_{2}O_{3}.

Explanation:

Aluminum has 33 valence electrons and loses them to become Al3+Al^{3+}. Oxygen has 66 valence electrons and gains 22 to become O2−O^{2-}. To balance the charges: 2×(+3)+3×(−2)=02 \times (+3) + 3 \times (-2) = 0. Therefore, two AlAl ions are needed for every three OO ions.

Problem 2:

Explain the bonding in a molecule of Nitrogen gas (N2N_{2}) using electron dot structures.

Solution:

Nitrogen forms a triple covalent bond: :N≡N::N \equiv N:

Explanation:

Each Nitrogen atom has 55 valence electrons. To reach a stable octet (88 electrons), each atom needs 33 more electrons. By sharing 33 pairs of electrons (a triple bond), both atoms achieve a full outer shell.

Problem 3:

Calculate the number of protons, neutrons, and electrons in a Magnesium ion (1224Mg2+^{24}_{12}Mg^{2+}).

Solution:

Protons=12,Neutrons=12,Electrons=10Protons = 12, Neutrons = 12, Electrons = 10

Explanation:

The atomic number Z=12Z=12 gives the number of protons. The mass number A=24A=24, so neutrons = 24−12=1224 - 12 = 12. Because it is a 2+2+ ion, it has lost 22 electrons from its neutral state (12−2=1012 - 2 = 10).