Chemistry Chapter on Metals and Ionic Compounds

Chemical Structures and Properties (Criterion 7)

• Chemical properties and the structures of atoms
  • The Periodic Table is structured based on electron configuration.
  • Elements in the same period or group have similar properties and reactivity.
  • Elements are organized into metals and non-metals.
  • Groups 1, 2, 17, and 18 have similar properties and common ionic charges.
  • Reactivity trends are observed in periods 2 and 3, and groups 1, 2, and 17.
  • Atomic properties, including bond formation, are explained by electron configurations.

Properties and Structures of Materials

• The type of bonding determines the physical properties of a substance.
• Metallic, ionic, and covalent substances have different structures and properties.
  • Chemical bonds form due to electrostatic attractions resulting from electron sharing or transfer.
  • Valency is a measure of the number of bonds an atom can form.
  • Ions are electrically charged atoms. Ionic bond formulas show constituent elements and charge.
  • Ionic compounds have high melting points, are brittle, and conduct electricity when molten or dissolved.
  • Metallic bonding involves a lattice of positively charged ions surrounded by mobile electrons.
  • Metallic properties (malleability, thermal/electrical conductivity) are due to this model.
  • Covalent substances are molecules or networks.
  • Intramolecular forces (strong bonds) are within molecules, while intermolecular forces (weak bonds) are between molecules.
  • Electron dot diagrams represent simple molecular compounds.

Chemical Properties of Metals

• Metals tend to lose electrons to form positive ions (cations), reacting with various chemical compounds.
• Losing electrons results in a similar electron configuration to a noble gas.
• Reactivity varies among metals; some lose electrons more easily (highly reactive).

Comparing Metals and Nonmetals

• Metals are lustrous, typically solid at room temperature, with high densities.
  • Good conductors of heat and electricity
  • Malleable and ductile.
  • Metallic oxides are basic.
• Nonmetals are not lustrous, can be solids, liquids, or gases, with low densities.
  • Poor conductors of heat and electricity.
  • Brittle in solid form.
  • Nonmetallic oxides are acidic.

Metallic Bonding

• Metallic bonding describes the bonding in metals.
• A metal lattice structure consists of closely packed metal ions surrounded by a 'sea' of delocalised electrons.
• Electrostatic attractions between these ions and electrons result in strong bonding, explaining high melting points, malleability, and ductility.

Properties of Metals

• Malleability and ductility are possible because of the delocalised electrons.
• Metals can conduct heat due to the delocalised electrons.
• Lustre is caused by the presence of free electrons.

Chemical Properties of Metals

• Metals react by losing electrons forming positive ions. (Cations)
• The result is the same electron configuration as a noble gas.
• Some metals lose electrons more easily than others, resulting in wide variance in reactivity.

Reactivity of Metals

• Reactivity of metals generally increases as you move down a group, like group 1 (alkali metals).
• As atomic radius increases down a group in metals, the valence electrons are further away from the nucleus, causing less attraction, making the metals more reactive.

Elements and the Periodic Table: Semi-metals

• Semi-metals have properties that are intermediate between metals and nonmetals.
• Some examples of semi-metals include boron, silicon, germanium, etc.

Elements and the Periodic Table: Nonmetals

• Nonmetals are generally poor electrical and thermal conductors and are typically not lustrous or malleable.
• They exist as solids, liquids or gases at room temperature.
• The reactivity of nonmetals varies considerably as you move down a given group.

Bonding and Chemical Compounds

• Chemical compounds are composed of two or more elements chemically bonded together.
• Chemical compounds have constant composition and properties.
• Ionic compounds are formed by the attraction between positive and negative ions.
• Covalent compounds contain covalent bonds and are formed when atoms share electrons.

Ionic Compounds (Naming and Formulae)

• Naming involves writing the cation (metal) first, followed by the anion (non-metal) with an ‘ide’ ending, sometimes with Roman Numerals for transition metals.
• Formulas balance positive and negative charges. Use the number of each ion in the chemical formula.

Ionic Compounds Containing Polyatomic Ions

• Polyatomic ions are groups of atoms with a charge.
• Names for polyatomic ions are fixed (for example, sulfate (SO42-), nitrate (NO3-), ammonium (NH4+)).
• For compounds with polyatomic ions, place the polyatomic ion in parentheses if there is more than one of the polyatomic ion in the formula.

Covalent Compounds (Naming and Formulae)

• Naming prefixes denote the number of atoms. Use prefixes to denote the number of atoms in the chemical formula. e.g. CO2 = carbon dioxide and N₂O₄ = dinitrogen tetroxide.

The Structure of Ionic Compounds

• Ionic compounds are 3-dimensional crystal lattices, not molecules, with repeating arrays of alternating cations and anions held together by electrostatic attraction.
• High melting and boiling points due to strong electrostatic forces.
• Hard but brittle. Not good conductors in solid form. Good conductors when dissolved in liquid or as aqueous solutions.

Covalent Compounds – Structures and Bonding

• Most covalent compounds are molecules that consist of discrete atoms.
• Covalent molecules have weak intermolecular forces (e.g., dispersion forces, sometimes dipole-dipole interactions, and hydrogen bonds) between molecules that influence melting and boiling points and other properties.
• Covalent lattices may form 3-dimensional networks.
• Strong covalent bonds throughout the lattice give them high melting points and inertness, like diamond.

Covalent Bonding: Different Elements

• The sharing of electrons in covalent bonds leads to molecules of specific shapes, and these have properties that are different from ionic or metallic compounds.
• Diatomic nonmetals form molecules in which two atoms share electron pairs to achieve a full outer shell. For instance, chlorine forms Cl2 molecules via a single electron pair shared between chlorine atoms.
• Oxygen forms O2 molecules by sharing two pairs of electrons (double bond).

Covalent Bonding: Drawing Diagrams (Lewis diagrams)

• Lewis structures use valence electrons only to show bonding atoms and unbonded electron pairs.
• The goal is to achieve a full outer electron shell (octet rule) for each atom, except hydrogen.

Forces in Covalent Molecular Bonding

• Dispersion forces are weak attractive forces that emerge from temporary changes in electron density within molecules.
• Polar molecules additionally have dipole-dipole attractions resulting from permanent partial positive and negative charges, and these often lead to higher boiling points than non-polar compounds.

Types of Formulae

• Molecular formula shows the exact number of atoms.
• Empirical formula shows the simplest ratio of atoms.
• Structural formula shows the bonds.
• Semi-structural formula shows some bonds but not all

Isomerism

• Isomers have the same molecular formula but different structures.
• Variations arise from differing arrangements of atoms. Different isomer forms result in difference of properties.

Homologous Series of Hydrocarbons

• A homologous series of hydrocarbons shows a pattern of recurring structural units, which leads to similar chemical and physical properties within the homologous series.
• These are classified as alkanes, alkenes, or alkynes, depending on whether they have single, double, or triple bonds, respectively.

Combustion of Hydrocarbons

• Complete combustion in plentiful oxygen produces carbon dioxide and water.
• Incomplete combustion in limited oxygen yields carbon monoxide and potentially carbon, as well as water.

Tests for Unsaturation

• Bromine water decolorization is used to distinguish saturated from unsaturated hydrocarbons.
• Saturated hydrocarbons typically do not decolorize bromine water, while unsaturated ones react rapidly, producing a colorless compound.

Naming Organic Compounds (IUPAC Nomenclature)

• Organic compounds are systematically named using the IUPAC system, which uses prefixes, stems, and suffixes.
• Prefixes specify the number of carbon atoms.
• Stems indicate the longest continuous chain of carbon atoms.
• Suffixes indicate the types of bonds (ane, ene, or yne).
• Side groups (substituents) are named and located with regard to the longest chain.