Periodic Trends
Does atomic radius increase or decrease as you move across a period from left to right?
Decrease
Write the electron configuration for oxygen, atomic number 8.
1s² 2s² 2p⁴
Is this reaction endothermic or exothermic?
Heat is released into the surroundings.
Exothermic
What number goes in front of O₂ to balance this equation?
2H₂ + ___O₂ → 2H₂O
1
What is Avogadro’s number?
6.02 × 10²³
Which atom has the larger atomic radius: Na or Cl?
Na
Does a positive ion form by gaining or losing electrons?
Losing electrons
Identify the reaction type:
2H₂ + O₂ → 2H₂O
Synthesis
Balance the equation:
Na + Cl₂ → NaCl
2Na + Cl₂ → 2NaCl
How many grams are in 2.00 moles of carbon?
Carbon molar mass = 12.01 g/mol
24.02 g
Does shielding effect increase or decrease as you move down a group?
Increase
Write the electron configuration for Na⁺.
1s² 2s² 2p⁶
Identify the reaction type:
2H₂O₂ → 2H₂O + O₂
Decomposition
Balance the equation:
Al + O₂ → Al₂O₃
4Al + 3O₂ → 2Al₂O₃
How many moles are in 36.04 g of water?
H₂O molar mass = 18.02 g/mol
2.00 mol H₂O
Which ion is larger: Na⁺ or Mg²⁺?
Na⁺
A chlorine atom gains 1 electron. What ion does it form?
Cl⁻
Identify the reaction type:
Zn + 2HCl → ZnCl₂ + H₂
Single replacement
Write the skeleton equation for:
Calcium reacts with oxygen to form calcium oxide.
Ca + O₂ → CaO
How many atoms are in 0.500 mol of helium?
3.01 × 10²³ atoms
Explain why atomic radius decreases across a period.
The nuclear charge increases, pulling electrons closer to the nucleus.
Explain what happens to the electron configuration when magnesium forms Mg²⁺.
Magnesium loses 2 valence electrons and becomes Mg²⁺ with the configuration 1s² 2s² 2p⁶.
Identify the reaction type:
CH₄ + 2O₂ → CO₂ + 2H₂O
Combustion
Balance the decomposition equation:
KClO₃ → KCl + O₂
2KClO₃ → 2KCl + 3O₂
Find the molar mass of calcium hydroxide, Ca(OH)₂.
Ca = 40.08, O = 16.00, H = 1.01
74.10 g/mol