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B. Matter, Chemical Trends, and Chemical Bonding · Matter, Chemical Trends, and Chemical Bonding

Matter, Chemical Trends, and Chemical Bonding: Unit Review

A1.1 A1.3 A1.4 A1.5 A1.6 A1.8 A1.9 A1.10 A1.11 A1.12 A1.13 A2.1 A2.2 B1.1 B1.2 B2.1 B2.2 B2.3 B2.4 B2.5 B2.6 B2.7 B3.1 B3.2 B3.3 B3.4 B3.5About 40 minutes
Learning goals
  • I can explain atomic structure, isotopes and relative atomic mass.
  • I can describe and explain periodic trends and the reactivity of metals and non-metals.
  • I can predict, draw and name ionic and molecular compounds and explain their properties.
  • I can evaluate the effects of common chemicals on health and the environment.

Words to know

isotope
Atoms of one element with different numbers of neutrons.
effective nuclear charge
The net positive charge felt by valence electrons.
electronegativity
An atom's ability to attract shared electrons in a bond.
ionic bond / covalent bond
Attraction between oppositely charged ions / a shared pair of electrons.
Lewis structure
A diagram showing bonds as lines and lone pairs as dots.
risk
The chance of harm, which depends on hazard and exposure.

Let's review!

In this unit you went from the inside of the atom to the chemicals in your kitchen. You described atoms with atomic and mass numbers, met isotopes and radioisotopes, and calculated relative atomic mass from isotopic abundance. You used effective nuclear charge and distance to explain the periodic trends in atomic radius, ionization energy, electron affinity and electronegativity, and you analysed real data across a period. You investigated how metals and non-metals react and built an activity series. Then you explained how ionic and covalent bonds form, drew Lewis structures, predicted bond type from electronegativity, built models of molecules and crystals, compared the properties of ionic and molecular compounds, and named compounds with IUPAC rules. Finally you analysed the environmental and health effects of common chemicals.

This review has a few questions from every lesson. Try each one, then press Show answer to check.

How to use this review

Do two or three sections at a time rather than all at once. Keep a periodic table and the electronegativity values from the bond-polarity lesson beside you. For calculations, show every step and round only at the end. For every question you get wrong, write down why (wrong trend direction? forgot to adjust electrons for charge? wrong naming rules?) and reread that lesson's worked examples. Finish with the 10-question quiz.

Inside the atomisotopes, radioisotopesrelative atomic massPeriodic trendsZeff and distanceradius, IE, EA, ENReactivitymetals, non-metalsactivity seriesBondingionic vs covalentΔEN, Lewis, modelsProperties and namesionic vs molecularIUPAC namesChemistry and societyenvironmenthuman healthHow the ideas in this unit connect
The unit at a glance. Atomic structure explains periodic trends, trends explain reactivity and bonding, and bonding explains properties and names, which we need to judge chemicals in society.

Atomic Number, Mass Number, Isotopes and Radioisotopes

1

Give the protons, neutrons and electrons in ⁵⁶₂₆Fe³⁺.

2

What is the difference between an isotope and a radioisotope?

3

A 200 mg sample of a radioisotope with a half-life of 2 days is stored for 8 days. How much remains?

Isotopic Abundance and Relative Atomic Mass

1

Neon is 90.48% Ne-20 (19.992 u), 0.27% Ne-21 (20.994 u) and 9.25% Ne-22 (21.991 u). Calculate its average atomic mass.

2

Why is the atomic mass of chlorine (35.45 u) closer to 35 than to 37?

3

An element has isotopes of 10.0 u and 11.0 u, and an average atomic mass of 10.8 u. Find the percentage of each.

Electron Arrangement, the Periodic Law and Effective Nuclear Charge

1

State the periodic law.

2

Estimate Zeff for the valence electrons of aluminium and of chlorine.

3

Why do elements in a group have similar chemical properties?

Trends in Atomic and Ionic Radius

1

Arrange in order of increasing radius: Rb, Li, K, Na.

2

Rank S²⁻, Cl⁻ and K⁺ from largest to smallest.

3

Explain why the radius decreases from Na to Cl.

Ionization Energy and Electron Affinity

1

Which has the higher first ionization energy, Mg or Ba? Why?

2

An element's ionization energies (kJ/mol) are 590, 1145, 4912, 6491. How many valence electrons does it have?

3

Which group releases the most energy when gaining an electron?

4

Write the equation for the first ionization of aluminium.

Electronegativity and Analysing Trends Across a Period

1

Rank by increasing electronegativity: Cl, Mg, Si, Na.

2

In period 3, which property rises to a peak at silicon and then falls?

3

Describe the trend in metallic character across a period and down a group.

periodic table (main groups)across: radius ↓ IE ↑ EN ↑ electron affinity ↑down:radius ↑IE ↓EN ↓F: highest ENCs: largest, lowest IEReason: Zeff rises across a period;distance (shells) rises down a group
Every periodic trend in this unit comes from two causes: effective nuclear charge increases across a period, and distance from the nucleus increases down a group.

Reactions of Metals and Non-metals: Building an Activity Series

1

Write a balanced equation for calcium reacting with water.

2

Is SO₂ an acidic or basic oxide? Write its reaction with water.

3

Metal Q reacts with acid but not with water; metal R does not react with acid. Which is higher in the activity series? Does Q displace R from a solution of R ions?

How Ionic and Covalent Bonds Form

1

Describe how potassium and sulfur form K₂S.

2

What holds the atoms together in a covalent bond?

3

How many electrons are shared in N₂?

Drawing Lewis Structures

1

How many valence electrons are in the Lewis structure of NO₃⁻?

2

Describe the Lewis structure of H₂S.

3

Describe the Lewis structure of C₂H₄.

Predicting Bond Type with Electronegativity

1

Classify: (a) Br–Br, (b) C–O, (c) Ca–Cl.

2

Which atom is δ− in an H–N bond?

3

Why is H₂O a polar molecule but CO₂ is not?

Molecular Models, Structural Formulas and Ionic Crystals

1

Name the shapes of CO₂, H₂O and CH₄.

2

How many Na⁺ ions surround each Cl⁻ ion in a sodium chloride crystal?

3

Write the structural formula of HCN.

Properties of Ionic and Molecular Compounds

1

Explain why CaCl₂ conducts electricity when dissolved, but solid CaCl₂ does not.

2

A substance melts at 80 °C and its solution does not conduct. Ionic or molecular?

3

Why do ionic crystals shatter when struck?

Just for fun

Chemistry review riddle: what do you call a tired ion that has given away all its valence electrons?

A little drained, but very positive.

IUPAC Names and Formulas: Ionic Compounds

1

Name: (a) Cu₂O, (b) NH₄NO₂, (c) Fe(ClO₄)₃.

2

Write formulas: (a) aluminium sulfate, (b) tin(II) fluoride, (c) barium chloride dihydrate.

3

What is the classical name for iron(III)?

IUPAC Names and Formulas: Molecular Compounds and Acids

1

Name: (a) PBr₅, (b) N₂O₄, (c) HBr(aq), (d) H₂SO₃(aq).

2

Write formulas: (a) carbon tetrafluoride, (b) perchloric acid.

3

Correct the name "calcium dioxide" for CaO.

Commonly Used Chemicals and the Environment

1

Name two properties that make a substance more likely to harm the environment.

2

Suggest one way to reduce the impact of road salt and explain why it helps.

3

Explain eutrophication in two sentences.

Chemicals and Human Health: Weighing Risks and Benefits

1

Distinguish hazard from risk.

2

Calculate the caffeine limit for a 48 kg teen (2.5 mg/kg/day).

3

Give one benefit and one risk of fluoride in toothpaste.

Check your understanding

Quiz

1.

How many neutrons are in an atom of ⁸⁸Sr (Z = 38)?

2.

An element has two isotopes: 60% with mass 70 u and 40% with mass 72 u. Its average atomic mass is

3.

Across a period from left to right, which property decreases?

4.

Which element has the lowest first ionization energy?

5.

Which metal reacts with cold water to produce hydrogen gas?

6.

Using EN values Mg 1.3 and O 3.4, the bond in MgO is

7.

How many lone pairs are on the nitrogen atom in NH₃?

8.

Which property is typical of molecular compounds?

9.

What is the correct name of Fe₂(CO₃)₃?

10.

Which statement about risk is correct?

For parents and teachers

How to use this review: Have your teen try each lesson's section without notes, then check. Wrong answers tell you which lesson to revisit:

  • Errors counting protons, neutrons or electrons, or with half-life: Atomic Number, Mass Number, Isotopes and Radioisotopes.
  • Weighted-average mistakes (percent vs decimal, simple average): Isotopic Abundance and Relative Atomic Mass.
  • Trend directions reversed, or explanations without a reason: Electron Arrangement, the Periodic Law and Effective Nuclear Charge, then the radius, ionization energy and electronegativity lessons.
  • Mixing up ionization energy and electron affinity, or misreading successive ionization energies: Ionization Energy and Electron Affinity.
  • Equation errors for metals with water, oxygen or acids, or activity series mix-ups: Reactions of Metals and Non-metals.
  • Calling NaCl a molecule, or confusing transfer and sharing: How Ionic and Covalent Bonds Form.
  • Wrong electron counts in Lewis structures: Drawing Lewis Structures (recount the total first).
  • ΔEN classification or polar bond vs polar molecule: Predicting Bond Type with Electronegativity.
  • Shapes and crystal structures: Molecular Models, Structural Formulas and Ionic Crystals.
  • Saying covalent bonds break when a molecular solid melts: Properties of Ionic and Molecular Compounds.
  • Naming errors: ionic (Roman numerals, brackets, hydrates) in Naming Ionic Compounds; prefixes and acids in Naming Molecular Compounds and Acids.
  • Weak risk-benefit answers: Commonly Used Chemicals and the Environment and Chemicals and Human Health.

This unit is the foundation for the rest of the course. Naming, formulas and bonding are used constantly in the Chemical Reactions and Quantities in Chemical Reactions units.