IB Chemistry: The Atom

IB Chemistry: The Atom

2.1 Atom

2.1.1 State the position of protons, neutrons and electrons in the atom

• Proton: Inside the nucleus
• Neutron: Inside the nucleus
• Electron: Orbiting the nucleus.

However, do note that the distance that the electron orbits the proton is VERY large. Visuzalize yourself where you are and pretend you are a proton. The electron will be two blocks away from you.

2.1.2 State the relative masses and relative charges of protons, neutrons and electrons.

2.1.3 Define the terms mass number (A), atomic number (Z) and isotopes of an
element.

Atomic Number (Z): This is determined by the number of protons in the nucleus of the element.

Mass Number (A): This is determined by the number of Protons + Neutrons inside the nucleus of the element, electrons have a small insignificant mass so it is ignored.

Isotopes: Atoms of the same element, with the same number of protons but with different number of neutrons.

2.1.4 Deduce the symbol for an isotope given its mass number and atomic number

2.1.5 Calculate the number of protons, neutrons and electrons in atoms and ions from the mass number, atomic number and charge.

First appreciate a few rules before you start calculating

• Number of proton never changes
• Electrons remain constant unless its an ion.
• Neutron depends on isotope you are dealing with.

Lets look at a few examples:

11B atom

Atomic Number: 5

Number of protons :5

Electrons: 5

Neutrons: 6

Na+ ion

Atomic Number: 11

Number of protons: 11

Neutrons: 12

Electrons: Here, it is a + ion, so there is one more proton than electron. However, the number of protons ALWAYS remains constant, so one electron is lost.

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Hence, there is 10 electrons.

2.1.6: Compare the properties of the isotopes of an element.

The properties of isotopes will be somewhat similar but will definitely have some differences, for example:

• Density
• Melting Points, Boiling Points
• Rate of diffusion

2.1.7 Discuss the uses of radioisotopes

Carbon Dating

This graph shows an example of carbon dating.

• Naturally occurring CO2 in the air contains some Carbon-14. The Carbon content of living things is continually replenished through absorption of CO2 so there is fixed ratio of Carbon-12 to Carbon 14.
• Once dead, Carbon 14 is no longer absorbed, and the remaining Carbon 14 goes under radioactive decay.
• The half life of carbon 14 is 5730 years. This is the time that a fixed amount of carbon 14 takes to decay to one half of the original amount. By measuring ratio of Carbon12 to Carbon 14 the age of something can be roughly estimated.

Medicine

• Cobalt 60
• Iodine 131
• Iodine 125

Cobalt 60 is a powerful gamma emitter and has been used for over 50 years to treat different types of cancer.

Additionally, Cobalt 60 can also:

• Sterilize medical equipment
• Food Irradiation
• Tracer for Cobalt in Chemical reactions.

Iodine 131 is used in the treatment of thyroid cancer.

Iodine 125 is used to treat prostate cancer and brain tumours.