The Atom

What are all things composed of

Matter

3 states of matter

Solid, liquid, gas

What are atoms

The fundamental unit of all elements

What is formed when element atoms group together

• Molecules

• Compounds

How many naturally occurring vs man-made elements is there that make up everything in the universe

• 94 naturally occurring

• 24 man-made

What 3 things do atoms consist of

• Protons (+ve charge)

• Neutrons (no charge)

• Electrons (-ve charge)

What is electric charge

A physical property of matter that causes it to experience a force when near other electrically charged matter

Where are protons and neutrons clustered and what are they called collectively

In the nucleus. Called nucleons

Where are the electrons

They orbit the nucleus

Who introduced the term “electron”?

George Stoney (Irish)

What is a Bohr diagram and who created it

A simplified 2D method of drawing atoms, created by Niels Bohr (1913)

What was the Bohr diagram conceived to reflect?

The “planetary model” first described by Rutherford in 1911

Why are ions important in radiography?

Ionisation in tissue can be dangerous

What happens when a Carbon atom is subjected to external energy and is now in an excited state and loses one electron

Still has 6 protons (charge of +6), but now has 5 electrons (charge of -5), therefore net charge becomes +6 - 5 = +1.

It is now a positive ion

What happens when Carbon is subjected ti an external interaction and is now in an excited state and gains one electron

6 protons (+6), 7 electrons (-7), net charge becomes +6 -7 = -1.

It is now a negative ion

Do neutrons and protons have approx. the same mass or not?

Yes

How wide is an atom, relatively speaking

The nucleus is tiny, ~1 millionth of a billionth of the full volume of the atom, but very dense as it contains virtually all the atom’s mass

What should the protons equal to in a relaxed atom?

Number of protons should be equal to number of electrons

What is the atomic number (Z) and what does it dictate

The number of protons in the atom, and this dictates the type of element

What is the atomic mass number (A)?

The number of protons and neutrons (nucleons) in the nucleus

How do you calculate the number of neutrons in an atom?

Atomic mass number (A) - Atomic number (Z)

Why is the atomic number sometimes not written in notation?

It contains the same information as the element symbol does, i.e. if it’s helium, atomic number MUST be 2, otherwise it wouldn’t be helium

How are the electrons arranged

In orbital shells

What is the first shell and how many electrons does it hold?

K shell, holds 2 electrons

What is the maximum number of electrons in any shell (formula)?

2n², where n is the shell number

What are the first 4 shells called and how many electrons do they hold?

K (2), L (8), M (18), N (32)

Why does the 2n² formula only hold exactly for the first 4 shells?

Due to the Aufbau principle - states that in the ground state of an atom or ion, electrons fill subshells of the lowest available energy, then they fill subshells of higher energy, e.g. the 1s subshell is filled before the 2s subshell is occupied

What does the Aufbau principle mean for the stability of an atom?

The electrons of an atom or ion form the most stable electron configuration possible

Configuration of Tungsten (W), Z = 74

• 2 x K Shell electrons … 2

• 8 x L Shell electrons …. 10

• 18 x M Shell electrons … 28

• 32 x N Shell electrons … 60

• 12 x O Shell electrons … 72

• 2 x P Shell electrons … 74

Why does the configuration of Tungsten not follow the 2n² formula after N Shell?

Due to the Aufbau Principle

What are isotopes?

Atoms with the same number of protons but different numbers of neutrons (e.g. ²³⁸₉₂U, and ²³⁵₉₂U)

How many isotopes do all elements have

More than one

Why are some isotopes unstable?

Too many or too few neutrons

How many elements have at least 1 stable isotope?

80, the rest are always radioactive

What happens with isotopes that are unstable?

They exhibit radioactivity in that they spontaneously emit particles & electromagnetic radiation

What 2 names are radioactive isotopes also known as?

• Radioisotopes

• Radionuclide (nuclide is a name for a specific isotope)

What are the 26 elements with only one stable isotope called?

Monoisotopic

How many stable isotopes does Tin have?

10, the largest number of stable isotopes known for an element

What do we get if we remove 3 protons from element ²⁰⁶₈₂Pb?

Au-203

If you remove 3 protons, they are deducted from Z (Making the Z = 79 and therefore it must be gold), BUT ALSO from atomic mass as protons form part of the mass