Atomic Structure and Isotopes

Question 1

John Dalton’s Billiard Ball Model

Answer 1

1. All matter is composed of tiny, invisible particles called atoms.
2. All atoms of an element have identical properties
3. Atoms of different elements have different properties.
4. Atoms of 2 or more elements can combine in constant ratios to form new substances.
5. In chemical Reactions, atoms join together or separate from each other but are not destroyed.

Question 2

J.J Thompson’s Plum Pudding Model

Answer 2

1. Atoms contain negativity charged electrons
2. Electrons are evenly distributed through the atom.
3. Atoms are neutral, so there must be positive charges to balance out the negative charges.

Question 3

Rutherford Gold Foil Experiment SUMMARY

Answer 3

1. Positively charged shot at a high speed. They predicted that the particles would pass through.
2. Some deflected at large angles or right back. This means that there is a like charge that repels the positive charge.

Question 4

Rutherford Gold Foil Experiment CONCLUSION

Answer 4

All of the atom’s positive charge and most of the atom’s mass were concentrated at a tiny point in the center (the nucleus). The electrons surrounded the nucleus + occupied most of the atom’s volume, but they only made up of a small fraction of the atom’s total mass.
- They came up with this conclusion b/c the atoms would not deflect and stick together.

Question 5

Chadwick’s Neutrons

Answer 5

1. Chadwick discovered that the nucleus contains neutral particles (neutrons) as well as positively charged particles (protons)
2. Each neutron in an atom has about the same mass as each proton in the same atom, but the neutron carries no electrical charge.

Question 6

Bohr’s Energy Levels

Answer 6

Bohr suggested that electrons surround the nucleus in specific energy levels, each of which can hold a specific # of electrons.

Question 7

Electrons

Answer 7

In a neutral atom, the number of electrons is equal to the number of protons
Neutrons balance the number of protons. We don’t use elections to classify atoms since we lose and gain.

Question 8

Neutrons

Answer 8

The number of neutrons in an atom of an element depends on the mass number of the nucleus
mass number = number of protons + number of neutrons

Question 9

Isotopes

Answer 9

Isotopes are different versions of elements due to the number of neutrons, changing the atomic mass. (ex. Hydrogen-1, Hydrogen-2)

Question 10

Average Atomic Mass

Answer 10

Average Atomic Mass (AAM)
is the weighted average mass of all the naturally occurring isotopes of that element.
(ex. Since there is way more hydrogen-1 than hydrogen-2, the average mass number of all hydrogen atoms in the universe is 1.01 )
This value is called the average atomic mass of hydrogen.
(The AAM is found on the periodic table, unit amu (μ - Greek symbol))

Question 11

AAM Formula

Answer 11

Average Atomic Mass = (Atomic Mass of Isotope A x Mass % of A) + (Atomic Mass of Isotope B x Mass % of B)…

Question 12

Mass Spectrometer

Answer 12

Scientists use a mass spectrometer to identify isotopes and their respective abundances
The sample is vaporized (converted to the gas phase by heating)
An electron beam bombards the vapors, which converts the vapors to ions
Because mass spectroscopy measures the mass of charged particles, only ions will be detected, and neutral molecules will not be seen.

Question 13

Parts of a Mass Spectrometer

Answer 13

Sample enters.
HEATER vaporizes the sample (turns the sample into gas)
ELECTRON BEAM SOURCE: bombards the vapors and converts the vapors into ions.
ions are accelerated
MAGNETS: Magnetic field deflects the lightest ions
DETECTOR: only ions are detected, not neutral-charged particles.

Question 14

Unstable Isotopes

Answer 14

Some isotopes are unstable!
Some isotopes are stable; others break apart easily
For example, O has 3 naturally occurring isotopes (O-16, O-17, and O-18) that are stable; but scientists have found 10 additional isotopes that are unstable and emit nuclear radiation

Question 15

Radioactive Decay

Answer 15

The disintegration of unstable isotopes is called radioactive decay
The emitted nuclear radiation can take the form of energy or very small particles

Question 16

Nuclear Radiation (Types of)

Answer 16

The most common types of nuclear radiation are:
Alpha (α) particles: positively charged particles with the same structure as the nucleus of a helium atom
Beta (β) particles: negatively charged particles identical to electrons
Gamma (γ) rays: a form of high-energy electromagnetic radiation

Question 17

Radioisotopes

Answer 17

Isotopes that decay to produce nuclear radiation are known as radioisotopes
For example, ALL of the isotopes of uranium are radioactive; there is no such thing as stable uranium!

Question 18

Useful Radioisotopes

Answer 18

Useful Radioisotopes :
- iodine-131
Used to treat an overactive thyroid gland
- americium-241
Used in smoke detectors
- cobalt-60
Food irradiation
- carbon-14 & potassium-40
Archeological dating

Question 19

Difference Between RadioIsotopes and Isotopes

Answer 19

The difference between an isotope and a radioisotope is that the latter is unstable. In other words,
radioisotopes undergo radioactive decay over time, producing nuclear radiation. Non-radioisotopes
do not do this.

Question 20

Extra: Carbon Dating with Carbon-14

Answer 20

Carbon-14 is radioactive, which means that it decays over time. So, the less carbon-14 present in a
fossil, the older it must be. Using math, scientists can predict the exact age of the fossil based upon
the specific amount of carbon-14 remaining. (We don’t learn this math in grade 11 chemistry).

Question 21

Octet Rule

Answer 21

The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds.