Unit 6A: Ionic and Covalent Bonding

Ions Why do elements in the same group behave similarly? They have the same number of valence electrons. Valence electrons are the electrons in the highest occupied energy level of an element’s atoms. How do you find the number of valence electrons in an atom of a representative element? The Group number.

Ions What are electron dot structures? Diagrams that show valence electrons as dots.

Ions Why do atoms form ions? In order to become more stable The octet rule states that in forming compounds, atoms tend to achieve the electron configuration of a noble gas. How do metals become stable? By losing their valence electrons How do nonmetals become stable? By gaining valence electrons By sharing valence electrons with other nonmetals

Ions How are cations formed? Cations are formed when an atom loses one or more electrons.

Ions How are anions formed? Anions are formed when an atom gains one or more valence electrons.

Ionic Bonds and Ionic Compounds What is an ionic compound? A compound that is composed of cations and anions. What is the electrical charge of an ionic compound? All ionic compounds are neutral What is an ionic bond? The electrostatic forces that hold cations and anions together in an ionic compound.

Ionic Bonds and Ionic Compounds How do chemists represent the composition of a substance? A chemical formula shows the kinds and numbers of atoms in the smallest unit of a substance. Examples: H 2 O C 12 H 22 O 11 Fe 2 O 3 CO 2

Ionic Bonds and Ionic Compounds The smallest unit of an ionic compound is called a formula unit. Lowest whole-number ratio of ions in an ionic compound Examples: Sodium chloride NaCl Magnesium chloride MgCl 2

Molecular Compounds Why do atoms form molecular compounds? To satisfy the octet rule How are atoms held together in covalent bonds? Sharing of valence electrons

Molecular Compounds What is a molecular formula? The chemical formula of a molecular compound It shows how many atoms of each element a molecule contains Examples: H 2 O CO 2 NH 3

Molecules Diatomic Molecule : A molecule consisting of only two atoms. There are seven diatomic elements: Hydrogen (H 2 ) Oxygen (O 2 ) Nitrogen (N 2 ) Fluorine (F 2 ) Chlorine (Cl 2 ) Bromine (Br 2 ) Iodine (I 2 )

The Nature of Covalent Bonding Single Covalent Bond An electron dot structure represents a covalent bond using dots to represent the shared pair of electrons.

The Nature of Covalent Bonding Unshared Electrons A pair of electrons not shared between atoms is called an unshared pair of electrons A structural formula represents covalent bonds by dashes and shows the arrangement of covalently bonded atoms.

The Nature of Covalent Bonding Double Covalent Bond

The Nature of Covalent Bonding Triple Covalent Bond

The Nature of Covalent Bonding

Polar Bonds and Molecules Polar Covalent Bond A polar covalent bond is a covalent bond in which the electrons are shared unequally. The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

Polar Bonds and Molecules Differences Between Types of Bonds Electronegativity Difference Bond Type Element Types Examples 0 – 0.4 Nonpolar Covalent Nonmetal- nonmetal H―H Cl―Cl 0.5 – 2.0 Polar Covalent Nonmetal- nonmetal H―Cl > 2.0Ionic Metal- nonmetal Na + Cl –