UPCAT Chemistry — Periodic Table, Bonding & Chemical LanguageFlash Cards

What is the trend for atomic size as you move across a period from left to right?

Atomic size DECREASES from left to right across a period. This happens because the number of protons increases, creating stronger nuclear attraction that pulls electrons closer to the nucleus. Example: Na > Mg > Al > Si > P > S > Cl

Calculate the number of valence electrons in sulfur (S) and predict its ion charge.

Step 1: S is in Group 16 (6A), so it has 6 valence electrons. Step 2: To achieve noble gas configuration, S needs 2 more electrons. Step 3: S gains 2 electrons to form S²⁻ ion. Answer: 6 valence electrons, forms S²⁻ ion

What type of bond forms between Mg and Cl₂? Write the balanced equation.

IONIC BOND forms between metal (Mg) and nonmetal (Cl). Balanced equation: Mg(s) + Cl₂(g) → MgCl₂(s). Mg loses 2 electrons to form Mg²⁺, each Cl gains 1 electron to form Cl⁻. Electrostatic attraction holds ions together.

Explain why NH₃ (ammonia) has a bent molecular geometry.

NH₃ has TRIGONAL PYRAMIDAL geometry, not bent. Using VSEPR theory: N has 3 bonding pairs (N-H bonds) and 1 lone pair. The lone pair takes up more space, pushing the H atoms closer together, creating a pyramid shape with bond angle ~107°.

Name the compound CaCl₂ and write the formula for aluminum oxide.

CaCl₂ = Calcium chloride (Ca²⁺ + 2Cl⁻). For aluminum oxide: Al³⁺ + O²⁻. Using criss-cross method: Al₂O₃. Steps: Al³⁺ needs 3 electrons, O²⁻ provides 2, so need 2 Al and 3 O for balance.

What type of intermolecular force exists between HF molecules?

HYDROGEN BONDING - the strongest type of dipole-dipole force. HF has highly polar H-F bond due to large electronegativity difference. H (δ+) of one HF molecule attracts F (δ-) of another HF molecule. This explains HF's high boiling point.

Draw the Lewis structure for CO₂ and determine if it's polar or nonpolar.

Lewis structure: O=C=O (linear). Steps: C has 4e⁻, each O has 6e⁻ = 16 total. C forms double bonds with each O. Molecular geometry is LINEAR. Although C=O bonds are polar, they cancel out due to symmetry. Result: NONPOLAR molecule.

Name the acid HClO₃ and write the formula for sulfurous acid.

HClO₃ = Chloric acid (from ClO₃⁻ chlorate ion, -ate becomes -ic). For sulfurous acid: comes from SO₃²⁻ sulfite ion (-ite becomes -ous), so formula is H₂SO₃. Remember: -ate → -ic acid, -ite → -ous acid

Why does ionization energy increase across a period?

Ionization energy increases across a period because: 1) Nuclear charge increases (more protons), 2) Atomic size decreases, 3) Electrons are held more tightly, 4) More energy needed to remove an electron. Example: Na < Mg < Al < Si < P < S < Cl

Name these binary covalent compounds: CO₂, N₂O₄, SF₆

CO₂ = Carbon dioxide. N₂O₄ = Dinitrogen tetroxide. SF₆ = Sulfur hexafluoride. Rules: First element keeps name, second gets -ide ending. Use prefixes: di- (2), tetra- (4), hexa- (6). Drop 'mono-' for first element.

Calculate formal charge of N in NH₃.

Formula: FC = valence e⁻ - nonbonding e⁻ - (bonding e⁻/2). For N in NH₃: Step 1: N has 5 valence e⁻, Step 2: N has 2 nonbonding e⁻ (1 lone pair), Step 3: N has 6 bonding e⁻ (3 bonds). FC = 5 - 2 - (6/2) = 0

What happens when sodium metal reacts with chlorine gas?

2Na(s) + Cl₂(g) → 2NaCl(s). This is an ionic bond formation reaction. Na loses 1 electron: Na → Na⁺ + e⁻. Each Cl gains 1 electron: Cl + e⁻ → Cl⁻. Results in crystalline salt with high melting point due to strong electrostatic forces.

Predict the molecular geometry of water (H₂O) using VSEPR theory.

H₂O has BENT molecular geometry. Steps: 1) O has 2 bonding pairs (O-H bonds), 2) O has 2 lone pairs, 3) Total = 4 electron pairs → tetrahedral electronic geometry, 4) 2 lone pairs push bonding pairs closer → bent shape with ~104.5° bond angle.

Write the formula for calcium phosphate using the phosphate ion PO₄³⁻.

Ca²⁺ + PO₄³⁻ → Ca₃(PO₄)₂. Steps: 1) Ca has +2 charge, PO₄ has -3 charge, 2) Need 3 Ca²⁺ and 2 PO₄³⁻ for charge balance, 3) 3(+2) + 2(-3) = 0. Parentheses needed around polyatomic ion with subscript >1.

Why do larger molecules have stronger London dispersion forces?

Larger molecules have MORE ELECTRONS that can shift to create temporary dipoles. More electrons = stronger temporary dipoles = stronger induced dipoles in neighboring molecules = stronger attractions. This explains why boiling points increase: CH₄ < C₂H₆ < C₃H₈ < C₄H₁₀.

Calculate the number of bonding and nonbonding electrons in NH₃.

Step 1: Total valence electrons = N(5) + 3H(1) = 8 electrons. Step 2: NH₃ has 3 N-H bonds = 6 bonding electrons. Step 3: Nonbonding electrons = 8 - 6 = 2 electrons (1 lone pair on N). Answer: 6 bonding, 2 nonbonding electrons.

Predict the bond type between H and F based on electronegativity difference.

H (2.1) and F (4.0): Δχ = 4.0 - 2.1 = 1.9. Since Δχ > 1.7, this forms an IONIC BOND (in compounds) or highly polar covalent bond (in HF molecule). F is much more electronegative, so electrons spend more time near F atom.

A compound has molecular formula C₆H₁₂O₆. What is its empirical formula?

Step 1: Find the ratio C₆:H₁₂:O₆ = 6:12:6. Step 2: Divide by GCD (6): 6÷6 : 12÷6 : 6÷6 = 1:2:1. Step 3: Empirical formula = CH₂O. This represents the simplest whole-number ratio of atoms.

Name the compounds FeO and Fe₂O₃ using proper nomenclature.

FeO = Iron(II) oxide. Fe₂O₃ = Iron(III) oxide. Since Fe is a transition metal with variable charges, use Roman numerals. In FeO: Fe has +2 charge. In Fe₂O₃: Fe has +3 charge. Always balance with O²⁻ to find metal charge.

How does temperature affect the rate of evaporation according to kinetic molecular theory?

Higher temperature increases evaporation rate because: 1) Molecules have higher kinetic energy, 2) More molecules have enough energy to overcome intermolecular forces, 3) More molecules escape from liquid surface to gas phase. KE ∝ Temperature (KMT Postulate 4).