Atomic Structure
What three particles make up an atom?
Protons, neutrons, and electrons.
Define isotope.
Atoms of the same element with same protons, different neutrons.
What is Avogadro’s number?
6.022×10^{23}
What is the molar mass of water?
18.0 g/mol of water.
Define significant figures.
Digits that reflect the precision of a measured value.
Where are protons, neutrons, and electrons located?
Protons & neutrons in nucleus; electrons in electron cloud
How do you calculate mass number?
Protons + neutrons.
1 mole of any element contains how many atoms?
6.022×10^23 atoms
Find the molar mass of Na2SO4.
142.1 g/mol.
How many sig figs are in 0.00450?
3
What does the atomic number represent?
Number of protons (and electrons in a neutral atom).
What stays the same and what changes in all isotopes of an element?
The number of protons stays the same, but the number of neutrons changes.
How many moles are in 56.3 g of magnesium? (Mg = 24.3 g/mol)
2.32 mol
Convert 3.45 moles of NaCl into grams. (NaCl = 58.5 g/mol)
202 g.
Round 12.347 g to 3 significant figures.
12.3 g.
Most of an atom’s volume comes from what?
The electron cloud.
Why is the atomic mass on the periodic table often a decimal?
It’s a weighted average of isotopes.
Convert 2.5 moles of water into number of molecules.
1.51×10^{24} molecules
How many grams are in 0.120 moles of AlF3?
10.1 g
When multiplying 2.35 × 4.0, how many sig figs should the answer have?
2 sig figs
In an atom where is the heaviest of its structure and why?
Inside the nucleus where the protons and neutrons subatomic particles are located
Carbon has isotopes 12C (98.89%) and 13C (1.11%). Calculate the average atomic mass.
12.01 amu
Why is the mole important in chemistry?
It links atomic scale to measurable lab amounts.
A sample has 8.65 moles of C2H4. How many grams is this?
242 g.
Why do chemists use sig figs?
To show certainty and reliability in measurements.