Flashcards · 8462 · Topic 2

Bonding, structure, and the properties of matter flashcards

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The three types of strong chemical bond and where each occurs: Ionic: compounds of metals with non-metals. Covalent: most non-metallic elements and compounds of non-metals. Metallic: metallic elements and alloys.
What happens to the electrons in ionic, covalent and metallic bonding?: Ionic: transferred from metal to non-metal. Covalent: shared in pairs. Metallic: delocalised and shared through the structure.
What attracts what in each type of strong bond?: Ionic: positive ions and negative ions. Covalent: the shared pair of electrons and the nuclei of both atoms. Metallic: delocalised electrons and positive metal centres. All are electrostatic attractions.
How do you decide the bond type from the elements present?: Metal + non-metal compound → ionic. Non-metal(s) only → covalent. Metal(s) only, element or alloy → metallic. A single noble gas → no strong bonds.
What type of bonding is in solder, an alloy of tin and lead?: Metallic. An alloy of metals is metallic, not ionic, even though it contains two elements.

Ionic bonding: particles involved and where it occurs: Oppositely charged ions, in compounds of a metal with a non-metal.
How does an ionic bond form?: Outer-shell electrons transfer: the metal atom loses electrons to form a positive ion, the non-metal atom gains them to form a negative ion. Then the oppositely charged ions attract by strong electrostatic forces.
Ion charges for Groups 1, 2, 6 and 7: Group 1: loses 1 → 1+. Group 2: loses 2 → 2+. Group 6: gains 2 → 2−. Group 7: gains 1 → 1−.
Magnesium oxide: what happens to the electrons, and which electronic structures result?: Mg (Group 2) loses 2 electrons → Mg²⁺. O (Group 6) gains 2 → O²⁻. Both ions have the electronic structure of neon, the nearest noble gas.
Sodium chloride: the electronic structures of the two ions: Na⁺: 2,8 (like neon). Cl⁻: 2,8,8 (like argon).
Conventions for an ionic dot and cross diagram: Dots for electrons from one atom, crosses for the other; usually outer shell only; each finished ion in square brackets with its charge.

Ionic compound (structure): A giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions. The forces act in all directions in the lattice.
Describe the structure of sodium chloride: Na⁺ and Cl⁻ ions alternate in a regular cubic lattice; each ion has six oppositely charged nearest neighbours. Ratio 1 : 1, and there are no separate NaCl molecules.
A model of an ionic compound has 10 potassium ions and 5 oxide ions. Empirical formula?: 10 : 5 = 2 : 1, so K₂O. Check: 2(+1) + (−2) = 0.
One limitation of a ball and stick model of sodium chloride: Any one: the sticks suggest bonds between particular pairs of ions, when forces act in all directions; ions are shown too far apart; sizes may be wrong; only a tiny part of the lattice is shown.
One limitation of a dot and cross diagram for an ionic compound: Any one: shows one pair of ions only; no 3D arrangement; no relative sizes; does not show the forces acting in all directions.
In a diagram, how do you tell an ionic structure from a metallic one?: Ionic: two types of particle, positive and negative ions. Metallic: positive particles among delocalised electrons, with no negative ions.

Covalent bond: A shared pair of electrons between two atoms. Covalent bonds are strong.
How many covalent bonds do H, C, N, O and Cl form?: H 1, C 4, N 3, O 2, Cl 1. For Groups 4 to 7: bonds = 8 − group number.
Nitrogen, N₂: shared and non-shared pairs: A triple bond (N≡N): 3 shared pairs, and 1 non-shared pair on each N.
Water, H₂O: shared and non-shared pairs: 2 shared pairs (two O–H bonds) and 2 non-shared pairs on the oxygen.
CO₂ and SiO₂: which structure is each?: CO₂: small molecules. SiO₂: giant covalent (each Si bonded to 4 O, each O to 2 Si). For a giant structure the formula gives only the ratio of atoms.
Polymer: A very large molecule made of many repeating units joined by covalent bonds.
A model shows 2 N atoms and 4 H atoms in one molecule. Molecular formula?: N₂H₄. A molecular formula gives the actual number of atoms: do not cancel it to NH₂.

Delocalised electrons (in a metal): Outer-shell electrons from metal atoms that are free to move through the whole structure.
Metallic bond: The strong bond that comes from sharing delocalised electrons among the metal atoms in a giant regular structure.
How are the atoms arranged in a metal?: A giant structure of atoms arranged in a regular pattern.
How many delocalised electrons does each atom of sodium, calcium and aluminium provide?: The number of outer electrons: sodium 1 (Na⁺ left), calcium 2 (Ca²⁺), aluminium 3 (Al³⁺).
Covalent vs metallic bonding: electrons and structure: Covalent: electrons shared in pairs between two particular atoms; small molecule, polymer or giant covalent. Metallic: electrons delocalised across the whole structure; always giant and regular.