Chapter 6 – Chemical Bonds

Section 6.1 – Ionic Bonds When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react. The noble gases have stable electron configurations with eight valence electrons (or two in the case of helium).

Stable Electron Configurations The chemical properties of an element depend on the number of valence electrons. An electron dot diagram is a model of an atom in which each dot represents a valence electron.

Ionic Bonds Some elements achieve stable electron configurations through the transfer of electrons between atoms. An atom that has a net positive or negative charge is called an ion.

Ions An ion with a negative charge is an anion. Anions like the Cl- ion are named by adding the suffix –ide to the element name. (Ex. Cl- = chloride) An ion with a positive charge is a cation. The name of a cation is the same as the element name. (Ex. Na+ = sodium)

Ion Charges The charges that an ion has are based on the number of valence electrons that an element has. All of the elements in the same group have the same charge.

Ion Charges Is it easier for lithium to gain 7 more electrons or lose 1 electron? What charge would lithium have? lose 1 electron +1

Ion Charges Is it easier for carbon to gain 4 more electrons or lose 4 electrons? What charge would carbon have? lose or gain 4 electrons +4 or -4

Ion Charges Is it easier for nitrogen to gain 3 more electrons or lose 5 electrons? What charge would nitrogen have? gain 3 electrons -3

Ion Charges Is it easier for oxygen to gain 2 more electrons or lose 6 electrons? What charge would oxygen have? gain 2 electrons -2

Ion Charges Would neon want to gain or lose electrons? What charge would neon have? No, it has a full energy level

Ion Charges Since elements in the same group have the same number of valence electrons, they all have the same charge.

Formation of Ionic Bonds A chemical bond is the force that holds atoms or ions together as a unit. An ionic bond is the force that holds cations and anions together. An ionic bond forms when electrons are transferred from one atom to another.

Formation of Ionic Bonds When an ionic bond is formed, electrons are transferred until each atom has a full outer energy level.

Ionic Compounds Compounds that contain ionic bonds are ionic compounds, which can be represented by chemical formulas. A chemical formula is a notation that shows what elements a compound contains and the ratio of the atoms or ions of these elements in the compound.

Crystal Lattices A chemical formula for an ionic compound tells you the ratio of the ions in the compound. Solids whose particles are arranged in a lattice structure are called crystals.

Properties of Ionic Compounds Ionic compounds tend to have high melting points (above 300oC). Ionic compounds are poor conductors in the solid state, but they can conduct heat or electricity when they are melted. Ionic compounds are brittle, so they shatter when struck by a hammer. The properties of ionic compounds can be explained by the strong attractions among ions within a crystal lattice. Form between a metal and a nonmetal

Ionic Compounds and Electricity

Day 2

Section 6.2 – Covalent Bonding A covalent bond is a chemical bond in which two atoms share a pair of valence electrons. When two atoms share one pair of electrons, the bond is called a single bond.

Covalent vs Ionic Bond

Molecules of Elements A molecule is a neutral group of atoms that are joined together by one or more covalent bonds. The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond. Many nonmetal elements exist as diatomic molecules. Diatomic means two atoms. They are H2, F2, Cl2, N2, Br2, O2, and I2.

Diatomic Elements

Multiple Covalent Bonds When two atoms share two pairs of electrons, the bond is called a double bond. When two atoms share three pairs of electrons, the bond is called a triple bond.

Properties of Bonds COVALENT IONIC Bond Formation e- are transferred from metal to nonmetal e- are shared between two nonmetals Type of Structure crystal lattice true molecules Physical State solid liquid or gas Melting Point high low Solubility in Water yes usually not Electrical Conductivity yes (solution or liquid) no C. Johannesson Other Properties Hard but brittle odorous

https://www.youtube.com/watch?v=DEdRcfyYnS Q https://www.youtube.com/watch?v=LkAykOv1foc

Day 3

Section 6.3 – Naming Compounds and Writing Formulas The name of an ionic compound must distinguish the compound from other ionic compounds containing the same elements. The formula of an ionic compound describes the ratio of the ions in the compound.

Binary Ionic Compounds A compound made from only two elements is a binary compound. When naming an ionic compound the name of the metal (cation) does not change and the name of the nonmetal (anion) has the suffix –ide. Ex. MgBr2 = magnesium bromide

Metal with Multiple Ions Many transition metals form more than one type of ion. When a metal forms more than one ion, the name of the ion contains a roman numeral to indicate the charge of the ion. Ex: Fe+2 = iron (II) Fe+3 = iron (III)

Polyatomic Ions A covalently bonded group of atoms that has a positive or negative charge and acts as a unit is a polyatomic ion.

WRITING FORMULAS FOR IONIC COMPOUNDS Place the symbol of the cation first, followed by the symbol of the anion. Use subscripts to show the ratio of the ions in the compound. Because all compounds are neutral, the total charges on the cations and anions must add up to zero.

Crossing Charges To balance the charges in an ionic compound, you can cross the charges if they are not the same.

Describing Molecular Compounds The name and formula of a molecular compound describe the type and number of atoms in a molecule of the compound. Molecular compounds only contain nonmetals.

Naming Molecular Compounds The name of the first element is the same. The name of the second element ends in the suffix -ide. Prefixes tell the number of atoms of each element. A prefix is not used when the first element only has 1 atom. Ex. CO2 = carbon dioxide

Prefixes 2 = di 7 = hepta 3 = tri 8 = octa 4 = tetra 9 = nona 1 = mono 6 = hexa 2 = di 7 = hepta 3 = tri 8 = octa 4 = tetra 9 = nona 5 = penta 10 = deca

Writing Molecular Formulas Write the symbols for the elements in the order the elements appear in the name. The prefixes indicate the number of atoms of each element in this molecule. Ex: diphosphorus pentoxide = P2O5

Day 4

Section 6.4 – The Structure of Metals In a metal, valence electrons are free to move among the atoms, so the cations are surrounded by a sea of electrons. A metallic bond is the attraction between a metal cation and the shared electrons that surround it.

Metallic Bonds The cations in a metal form a lattice that is held in place by strong metallic bonds between the cations and the surrounding valence electrons. The more valence electrons an atom can contribute to the shared pool, the stronger the metallic bond will be.

Properties of Metals The mobility of electrons within a metal lattice explains the fact that metals are good conductors and malleable.

Alloys An alloy is a mixture of two or more elements that have metallic properties.

METALLIC Types of Bonds e- are delocalized among metal atoms Bond Formation e- are delocalized among metal atoms Type of Structure “electron sea” Physical State solid Melting Point very high Solubility in Water no yes (any form) Electrical Conductivity Other Properties malleable, ductile, lustrous