Unit 1: Topic 1 Periodic Table and Trends Flashcards
Q: How are elements represented?
A: By chemical symbols (e.g., H, He, Li).
Q: What is the basis for the periodic table’s structure?
A: Arranged by increasing atomic number.
Q: What are the four blocks of the periodic table?
A: - s-block: Groups 1 & 2
p-block: Groups 13–18
d-block: Transition metals
f-block: Lanthanides & actinides
Q: How does the periodic table relate to electron configuration?
Groups (columns) share the same number of valence electrons, determining chemical properties.
Periods (rows) indicate the number of electron shells.
Blocks (s, p, d, f) correspond to the type of orbital being filled.
Q: What periodic trends exist?
Atomic radius: Decreases across a period, increases down a group.
Ionisation energy: Increases across a period, decreases down a group.
Electronegativity: Increases across a period, decreases down a group.
Metallic character: Decreases across a period, increases down a group.
Atomic radius
Decreases across a period, increases down a group
Ionisation energy
the amount of energy required to remove an electron from an isolated atom
Increases across a period, decreases down a group.
Electronegativity
a measure of an atom’s ability to attract shared electrons to itself
Increases across a period, decreases down a group
Metallic character
Decreases across a period, increases down a group
Q: How does reactivity change for alkali metals ?
Reactivity increases down the group.
Q: How does reactivity change for halogens?
Reactivity decreases down the group
Q: How do period 3 oxides change across the period?
A: Basic → Amphoteric → Acidic
- Basic Oxides (Left of Period 3)
Found in Group 1 & 2 metals (e.g., Na₂O, MgO).
These oxides react with water to form basic solutions (alkalis)
or with an acid to form a salt and water in a neutralization reaction
- Amphoteric Oxides (Middle of Period 3)
Amphoteric oxides – Typically formed by metalloids and some transition metals (e.g., Al, Zn, Sn, Pb). They can react with both acids and bases to form salt and water (acidic reaction) or complex salts (basic reaction).
Reaction with acids: Amphoteric oxides behave like bases, reacting with acids to form a salt and water.
Reaction with bases: Amphoteric oxides behave like acids, reacting with strong bases (e.g., NaOH, KOH) to form complex salts (metalates or hydroxometalates).
Example:
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (acidic reaction)
Al₂O₃ + 2NaOH + 3H₂O → 2Na[Al(OH)₄] (basic reaction)
- Acidic Oxides (Right of Period 3)
Found in non-metals (e.g., SO₂, P₄O₁₀).
react with bases to form salts and water, or react with water to form acidic solutions.
What is the difference between an acid and a base
Acids donate H⁺, bases accept H⁺.
Acids have a pH < 7, bases have a pH > 7.
Acids taste sour, bases taste bitter and feel slippery.
Acids turn blue litmus red, bases turn red litmus blue.
What is effective nuclear charge (ENC)?
Effective Nuclear Charge (ENC) is the net positive charge an electron feels in an atom. It is calculated as the atomic number - the shielding effect of inner electrons.
Effective Nuclear Charge trend?
Across a Period: ENC increases because protons are added, but shielding remains relatively constant. This causes a stronger attraction to outer electrons, reducing atomic radius.
Down a Group: ENC stays relatively constant because both protons and shielding electrons increase, so outer electrons feel a similar net attraction.
what is an oxide?
An oxide is a compound that contains oxygen bonded to another element. Oxides can be classified based on the nature of the element they are bonded to:
Basic oxides – Formed by metals, typically from Groups 1 (alkali metals) and 2 (alkaline earth metals). They react with acids to form salt and water.
Acidic oxides – Formed by non-metals, often from Groups 14-16. They react with bases to form salt and water.
Amphoteric oxides – Typically formed by metalloids and some transition metals (e.g., Al, Zn, Sn, Pb). They can react with both acids and bases to form salt and water (acidic reaction) or complex salts (basic reaction).
Neutral oxides – Do not react with acids or bases, often formed by non-metals in low oxidation states.
from bonding:
What is Empirical formula
The empirical formula of a chemical compound isthe simplest whole number ratio of atoms present in a compound.
from bonding:
What is molecular formula
A chemical formula for a compound existing as discrete molecules that gives the total number of atoms of each element in a molecule. the molecular formula for water is H2O.
From bonding:
What is formula unit
A formula unit isthe smallest unit of a non-molecular substance, such as an ionic compound, covalent network solid, or metal.
From bonding:
Note about formula unit and molecular unit
The empirical formula and formula unit are interchangeable, but “formula unit” is preferred for non-molecular compounds (e.g., salts), while “empirical formula” is used for molecular compounds (e.g., water).
