Atomic Structure, Periodic Table and Chemical Bonding
Atomic Structure, Periodic Table and Chemical Bonding asks you to connect subatomic particles to electron arrangement, then to position in the periodic table and to the type of bond formed.
Atomic structure
- An atom has protons and neutrons in the nucleus and electrons in shells around it. Atomic number Z = number of protons; mass number A = protons + neutrons.
- Isotopes have the same Z but different A; they have identical chemical properties but different masses.
- Electrons fill shells in the order 2, 8, 8 for the elements studied. The outermost-shell electrons determine valency.
Periodic table
- Periods are horizontal rows; groups are vertical columns. Elements in the same group have the same number of valence electrons and similar chemical properties.
- Metals tend to lose electrons; non-metals tend to gain or share electrons. Noble gases have stable outer shells.
Bonding
- Ionic bonding: transfer of electrons from a metal to a non-metal, producing oppositely charged ions held by electrostatic attraction.
- Covalent bonding: sharing of electron pairs between non-metal atoms.
Worked example
Sodium has Z = 11 and electron arrangement 2, 8, 1; chlorine has Z = 17 and arrangement 2, 8, 7. Sodium loses its one valence electron to form Na+, chlorine gains one electron to form Cl-. The ions attract electrostatically, so sodium chloride is an ionic compound with formula NaCl.
Traps
- Confusing atomic number with mass number.
- Assuming isotopes have different chemical behaviour.
- Writing NaCl as a covalent molecule rather than an ionic lattice.
- Counting inner-shell electrons as valence electrons.