The Atom: From Philosophical Idea to Scientific Theory
What are the 2 important concepts of Dalton's atomic theory?
1. all matter is composed of atoms
2. Atoms of any one element differ in properties from atoms of another element remain unchanged
What is an atom?
The smallest particle of an element that retains the chemical properties of that element.
How are isotopes of a particular element alike?
They have the same number of protons and electrons.
Write the hyphen notation for the following isotope:
atomic number = 19
mass number = 39
potassium-39
What is an electron and where is it located?
A small, negatively charged particle of small mass found outside the nucleus.
According to the law of conservation of mass, if element A has an atomic mass of 2 units and element B has an atomic mass of 3 units, what mass would be expected for compound A2B3?
13 mass units
When neutrons are very close to each other or when protons and neutrons are very close together, what are the forces that hold the particles together called?
Nuclear forces
How many particles are in one mole?
6.022 x 1023
How many moles of atoms are there in 3.25 x 105 g Pb?
1.57 x 103 mol
What is the relative atomic mass of an atom?
The mass of an atom as it compares with the mass of a carbon-12 atom.
Explain the law of conservation of mass in terms of Dalton's atomic theory.
Because all chemical reactions are only the rearrangements of atoms, mass is neither created nor destroyed.
What number uniquely identifies an element?
The atomic number
What is the atomic mass of an atom if its mass is approximately 4.5 times as much carbon-12?
54 amu
How many atoms are there in 7.02 g Si?
1.50 x 1023 atoms
Who is credited with the discovery of the atomic nucleus?
Ernest Rutherford
Explain the law of definite proportions in terms of Dalton's atomic theory.
Atoms of each element have their own characteristic mass, so compounds consisting of these atoms always have the same composition by mass.
Describe at least 2 properties of electrons that were determined based on the experiments of Thomson and Millikan.
Must have 2 of the following:
1. An electron is negatively charged
2. has a mass approximately 1/2000 that of a hydrogen atom
3. has a fixed charge-to-mass ratio
4. is present in atoms of all elements
What is the definition of a mole?
The number of particles equal to the number of atoms in exactly 12 g of carbon-12
What is the mass in grams of 8.42 x 1018 atoms Br?
1.12 x 10-3 g
Determine the mass in grams of 4.86 x 1024 atoms Au.
1.59 x 103 g
Explain the law of multiple proportions in terms of Dalton's atomic theory.
Only whole atoms combine in chemical compounds, so different compounds between the same two elements must result from the combination of different whole numbers of atoms.
Summarize Rutherford's model of the atom, and explain how he developed this model based on the results of his famous gold-foil experiment.
His model had most of the mass in the nucleus. He bombarded gold atoms with positively charged particles; most went straight through the atom, but some were deflected and a few bounced back.
How is the mass in grams of the element converted to number of atoms?
Divide by molar mass, then multiply by Avogadro's number
Naturally occurring boron is 80.20% boron-11 (atomic mass = 11.01 amu) and 19.80% of some other isotopic form of boron. What must the atomic mass of this second isotope be in order account for the 10.81 amu average atomic mass of boron? (Write the answer to 2 decimal places)
10.00 amu
Calculate the number of moles in 45.0 g of acetic acid, CH3COOH.
0.749 mol CH3COOH