Bonding
Why is chlorine (Cl₂) a gas at room temperature, but sodium chloride (NaCl) is a solid crystal?
Cl₂ has weak intermolecular forces (van der Waals) → gas. NaCl has strong ionic bonds in a giant lattice → solid.
Why does adding lemon juice (acidic) to fish reduce its “fishy” smell?
The basic amines in fish react with citric acid in lemon → form ammonium salts, which are not volatile → smell is reduced.
Why is helium (He) unreactive, even though hydrogen (H₂) and oxygen (O₂) form many compounds?
Helium has a full outer shell (1s²) → very stable, no need to share or gain electrons, so it is chemically inert.
Why does salt (NaCl) melt ice on the roads in winter?
Salt dissolves in water and lowers the freezing point (freezing point depression, a colligative property) → prevents ice formation.
Why do cold drinks “fizz” when you open the bottle, but go flat if left open?
Carbon dioxide is dissolved under pressure. Once opened, pressure drops → CO₂ escapes → bubbles form. If left open, equilibrium shifts and all CO₂ leaves → no fizz.
Why does methane (CH₄) always form a tetrahedral shape, even though the carbon atom is “just one” element?
Carbon undergoes sp³ hybridization → four identical orbitals arrange tetrahedrally to minimize electron repulsion.
When you inhale carbon monoxide (CO), it binds strongly to hemoglobin in your blood.
Which orbital interaction explains why CO binds more strongly than O₂?
CO donates electrons from its filled lone pair orbital into hemoglobin’s Fe²⁺ empty orbital, and back-bonding occurs from Fe²⁺ d-orbitals into CO’s antibonding orbital, creating a stronger bond than with O₂.
When milk turns sour, it becomes acidic.
Which chemical concept explains why adding a little baking soda (a base) can neutralize this sourness?
Neutralization reaction. The weak acid in sour milk (lactic acid) reacts with sodium bicarbonate (baking soda), producing salt, water, and carbon dioxide gas. This reaction reduces acidity and balances the pH.
Why does copper chloride (CuCl₂) produce a green-blue color, while strontium chloride (SrCl₂) produces a red color in fireworks?
Different metal ions have different electron energy levels. The energy released when electrons return to ground state corresponds to different wavelengths of visible light.
You have 50.0 grams of table sugar, C12H22O11.
Calculate the molar mass of C12H22O11. (Atomic masses: C≈12.01 g/mol, H≈1.01 g/mol, O≈16.00 g/mol)
How many moles of sugar do you have?
Moles=Molar /Mass
Mass=342.34 g/mol
50.0 g/342.34≈0.146 moles
I’m how you find how much you’ve got,
In lemon juice or acid shot.
I measure drops you’ve never seen—
Who am I?
Moles
A neutral atom has an electron configuration of 1s22s22p63s23p4.
What element is this?
How many unpaired electrons does this atom have in its ground state, and in which orbital(s) are they located?
The electron configuration 1s22s22p63s23p4 has 2+2+6+2+4=16 electrons. A neutral atom with 16 electrons is Sulfur (S).
The valence configuration is 3s23p4. According to Hund's rule, the four electrons in the 3p sublevel are distributed as follows: three electrons are placed in separate 3p orbitals before the fourth electron is paired. This leaves two unpaired electrons in the 3p orbitals.
A chemist needs to prepare 2.50 L of a 0.750 M potassium nitrate (KNO3) solution. What mass (in grams) of KNO3 must be measured out and dissolved?
(Molar mass of KNO3≈101.11 g/mol)
Mass=1.875 mol×101.11 g/mol=189.58 g
A sample of calcium carbonate, CaCO3, contains 3.011×1023 formula units.
How many moles of CaCO3 are present in the sample?
What is the mass of the CaCO3 sample in grams? (Molar mass of CaCO3≈100.09 g/mol)
Mass=Moles×Molar
Mass=0.5000 mol×100.09 g/mol=50.05 g
A student dissolves 14.61 grams of sodium chloride (NaCl) in enough water to make a 500.0 mL solution. What is the molarity of the NaCl solution?
(Molar mass of NaCl≈58.44 g/mol)
M=0.5000 L/0.2500 mol=0.5000 M