Unit 1 Trends in properties of elements in the periodic table
Key unit competence: Analyse the trends and patterns in the properties of elements across periods and down groups to explain their periodic behaviour.
Key ideas
- Elements are classified as metals (left and centre), non-metals (right) and metalloids (B, Si, Ge, As, Sb, Te) along the staircase line, which have properties in between.
- Physical properties of metals: shiny (lustrous), good conductors of heat and electricity, malleable, ductile, sonorous, high melting points (except mercury) and high density. Non-metals are dull, brittle when solid, poor conductors (except graphite) and have low melting points.
- Reactivity of metals increases down a group (outer electrons further from nucleus, lost more easily) and decreases across a period. Reactivity of non-metals (halogens) decreases down a group and increases across a period (electrons gained more easily by small atoms).
- Chemical properties of metals: react with oxygen to form basic oxides, with water/steam to form hydroxides or oxides and hydrogen, with dilute acids to form a salt and hydrogen. Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Ag > Au.
- Chemical properties of non-metals: react with oxygen to form acidic or neutral oxides (CO2, SO2, CO), do not react with dilute acids, and gain electrons to form negative ions.
- Uses: copper for wires, aluminium for cooking pots and aircraft, iron for building (steel), gold for jewellery; carbon (graphite) for electrodes, sulfur for sulfuric acid, chlorine for water treatment, silicon for chips and solar cells.
Common misconceptions
- "All metals are hard solids." No: Mercury is liquid and sodium is soft enough to cut with a knife.
- "All non-metals are gases." No: Carbon, sulfur and phosphorus are solid non-metals; bromine is liquid.
- "Copper reacts with dilute hydrochloric acid like zinc." No: Copper is below hydrogen in the reactivity series and does not displace hydrogen from dilute acids.
Worked examples
Example 1. Give three differences between the physical properties of metals and non-metals.
Solution
Metals are shiny; non-metals are usually dull.
Metals conduct heat and electricity; non-metals do not (except graphite).
Metals are malleable and ductile; solid non-metals are brittle.
Example 2. Explain why reactivity increases down group 1 but decreases down group 17.
Solution
Group 1 metals react by LOSING an electron; down the group atoms get larger, the outer electron is further from the nucleus and is lost more easily, so reactivity increases.
Group 17 non-metals react by GAINING an electron; larger atoms attract an extra electron less strongly, so reactivity decreases.
Practice questions
Name two metalloids.
Show answer
Any two of boron, silicon, germanium, arsenic, antimony, tellurium.
Common mistake: Naming aluminium.
State four physical properties of metals.
Show answer
Shiny, good conductors, malleable, ductile, sonorous, high m.p. (any four).
Common mistake: Including 'brittle'.
Write the word equation for zinc and dilute sulfuric acid.
Show answer
Zinc + sulfuric acid → zinc sulfate + hydrogen.
Common mistake: Writing water as a product.
Why is graphite unusual among non-metals?
Show answer
It conducts electricity (delocalised electrons).
Common mistake: Saying it is shiny like a metal only.
Give the trend in reactivity of halogens down the group.
Show answer
Reactivity decreases from fluorine to iodine.
Common mistake: Saying it increases like group 1.
Name the products when calcium reacts with water.
Show answer
Calcium hydroxide and hydrogen.
Common mistake: Saying calcium oxide and oxygen.
Explain why copper is used to make electric cables.
Show answer
Good conductor of electricity, ductile and does not corrode easily.
Common mistake: Saying because it is cheap only.
Write the balanced equation for magnesium burning in oxygen.
Show answer
2Mg + O2 → 2MgO.
Common mistake: Writing MgO2.
Arrange in increasing reactivity: Fe, K, Cu, Mg.
Show answer
Cu < Fe < Mg < K.
Common mistake: Putting copper above iron.
Predict, with a reason, whether silver reacts with dilute HCl.
Show answer
No; silver is below hydrogen in the reactivity series.
Common mistake: Saying yes because all metals react with acids.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Across period 3 from Na to Cl, the elements become: a. Graphite (carbon) 2. Which halogen is the most reactive? b. Fluorine 3. Sodium is stored under paraffin oil because: c. less metallic 4. Which non-metal conducts electricity? d. it reacts quickly with air and water Show answer
1 → c (less metallic) · 2 → b (Fluorine) · 3 → d (it reacts quickly with air and water) · 4 → a (Graphite (carbon))
- Metallic character decreases across a period.
- Reactivity decreases down group 17; fluorine is at the top.
- Paraffin keeps air and moisture away.
- Graphite has delocalised electrons.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
basic · increases · hydrogen · decreases- Metals react with dilute acids to produce a salt and .
- Oxides of metals are generally .
- Down group 1, the reactivity of the metals .
Show answer
1: hydrogen · 2: basic · 3: increases
- Metal + acid → salt + hydrogen.
- Metal oxides react with acids; soluble ones form alkalis.
- The outer electron is further from the nucleus and lost more easily.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Which metal is used for electrical wiring? a. Good conductor of electricity 2. Which property is typical of metals? b. conducts heat well, is light and resists corrosion 3. Aluminium is used for cooking pans because it: c. Sulfur 4. Which element is a non-metal? d. Copper Show answer
1 → d (Copper) · 2 → a (Good conductor of electricity) · 3 → b (conducts heat well, is light and resists corrosion) · 4 → c (Sulfur)
- Copper is an excellent conductor and ductile.
- Metals have free electrons that carry current.
- A thin oxide layer protects aluminium.
- Sulfur is a yellow, brittle non-metal.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
broken easily · magnesium oxide and hydrogen · hammered into thin sheets · mercury- Magnesium reacts with steam to give .
- Malleable means a substance can be .
- The only metal that is liquid at room temperature is .
Show answer
1: magnesium oxide and hydrogen · 2: hammered into thin sheets · 3: mercury
- Mg + H2O → MgO + H2.
- Ductile means drawn into wires.
- Mercury melts at −39 °C.