Study Notes for Chapter Three: Ionic Compounds

Ions are electrically charged atoms formed by the gain or loss of electrons.
Cations: Positive ions, formed when an atom loses one or more electrons.
- Example: Sodium ion (Na+) indicates that a sodium atom has lost 1 electron.
Anions: Negative ions, formed when an atom gains one or more electrons.
- Example: Sulfide ion (S2-) indicates that a sulfur atom has gained 2 electrons.

Cation: A positive ion. The mnemonic for cations is that "cation" contains a 't', resembling the symbol for positive charge (+).
Anion: A negative ion.
Key Concept: Ions are identified not just by their charge but also by their ability to form compounds through ionic bonding.

Atoms engage in chemical reactions to achieve the same electronic configuration as the nearest noble gas, specifically the same number of electrons, not literally the same distance on the periodic table.
Achieving noble gas configuration leads to stability in the atoms.

This chapter will focus primarily on reactions where atoms gain or lose electrons to form ions.

Predict the ion formation when different atoms react:
- a) Magnesium (Mg): Forms Mg2+
- b) Bromine (Br): Forms Br−
- c) Phosphorus (P): Forms P3−
- d) Potassium (K): Forms K+

Atomic Radius: The distance from the nucleus to the outer boundary of the electron cloud.
Ionization Energy: The energy required to remove one electron from a neutral atom in the gaseous phase.
Electron Affinity: The tendency of an atom to attract additional electrons, reflecting its ability to gain electrons in a reaction.

Down a Group: Atomic radius increases due to the addition of energy levels (higher orbitals are larger).
Across a Period: Atomic size decreases because of increasing positive charge in the nucleus attracting electrons more strongly, reducing the radius.

As protons in the nucleus increase across a period, the electrical pull on electrons is stronger, making the atom smaller.
However, down a group the addition of energy levels increases the distance between nucleus and outer electrons, leading to larger atoms.

Across a Period: Ionization energy increases because electrons are held more tightly as atomic number rises.
Down a Group: Ionization energy decreases because increased distance from the nucleus makes electron removal easier due to shielding.
- Summary: Ionization energy tends to increase going up and to the right on the periodic table.

Across a Period: Electron affinity increases because electrons are attracted more strongly as the nuclear charge increases.
Down a Group: Electron affinity decreases due to increased distance from the nucleus leading to weaker attraction for additional electrons.
- Summary: Electron affinity increases upwards and to the right on the periodic table.

Noble gases show very low tendencies to gain or lose electrons, resulting in high ionization energies and low electron affinities.
Noble gases typically do not participate in bonding due to their filled valence shells.

When sodium metal (Na) reacts with chlorine gas (Cl2), the reaction produces sodium chloride (NaCl), commonly known as table salt.
Representation:
- Sodium’s electron configuration: Na (1s² 2s² 2p⁶ 3s¹) reacts by losing one electron, becoming Na+.
- Chlorine’s electron configuration: Cl (1s² 2s² 2p⁶ 3s² 3p⁵) reacts by gaining one electron, becoming Cl−.

The transfer of an electron from sodium to chlorine results in the formation of ions (Na+ and Cl−) which are held together by ionic bonds due to their opposite charges.
An ionic compound contains ionic bonds and remains electrically neutral overall.

Physical State: Ionic compounds are typically solid at room temperature.
Electrical Conductivity: In solution, ionic solids dissolve and allow ions to move freely, enabling conductivity.
Melting and Boiling Points: Ionic compounds often have high melting (e.g., NaCl melts at 801ºC) and boiling points (e.g., boils at 1413ºC).
Brittleness: Ionic compounds can shatter when subjected to force due to their rigid crystal structure.

Ionic compounds are composed of the lowest whole number ratios of cations and anions such that the total charge equals zero.
Example formulas:
- Zn2+ and Cl− combine to form ZnCl2.
- Na+ with O2− forms Na2O.
- Mg2+ with P3− forms Mg3P2.

Variable charges for cations must be indicated by Roman numerals in their names:
- Metals in group 1 form cations with a charge of 1+.
- Metals in group 2 form cations with a charge of 2+.
- Aluminum (Al) forms a cation with a charge of 3+.
- Zinc (Zn) and cadmium (Cd) form cations with 2+. Silver (Ag) forms a cation with 1+.

Anions usually have fixed charges based on their group placement; group 15 elements typically have a charge of 3-, group 16 have 2-, and group 17 have 1-.

Definition: Ions that contain more than one atom.
- Example: Sulfate ion, SO4²−. The charge applies to the entire grouping of atoms.
- Important Note: Polyatomic ions retain their names when forming compounds; their endings do not change.

Determined by the cation first, then the anion.
Cations with ONE charge: Names are identical to the metal name.
- Example: Mg2+ is magnesium ion.
Cations with VARIABLE charge: The name of the metal accompanied by its charge in Roman numerals.
- Example: Iron(II) chloride indicates iron has a 2+ charge.

Acids: Yields H+ ions in water (e.g., HCl, H2SO4).
Bases: Yields OH− ions in water (e.g., NaOH, Ca(OH)2).
- Basic solutions are also termed alkaline.
**Properties of Acids and Bases:
- Acids can denature proteins, are corrosive, neutralize bases, and change indicator colors.
- Bases also denature proteins, neutralize acids producing water, and exhibit color changes in indicators.

Ions: Atoms are converted to cations or anions by losing or gaining electrons, respectively.
Ionic Compounds: Composed of cations and anions, exhibit electrical conductivity in solutions, and possess typically high melting and boiling points.
Reactivity: Main group elements adjust their electron counts to resemble the nearest noble gas for stability, thus forming ions according to their group placement on the periodic table.
Naming and Formula Composition: Cations take the metal's name; anions receive the -ide suffix, and charges must be accurately reflected in compound names.