2.4 - Nuclear Model

The theory of atomic structure is known as

The Nuclear Model

What does this model suggest?

That the atom consists of:

• a very small and extremely dense region called the nucleus; and

• a cloud of negative electrically charged particles surrounding the nucleus at a distance

The nucleus is _________ when compared to the rest of the whole atom

very small

What does this model also suggest?

That the atom consists of three smaller sub-atomic particles

What are these sub-atomic particles?

Protons, Neutrons and Electrons

Since these particles are extremely small and light, and therefore cannot be measured in grams, what is used instead

atomic mass units (amu)

Fill in this table

In more detail, explain where and how electrons are found.

• Electrons are found moving at a very high speed around the nucleus

• Electrons exist in different shells; each shell has a different amount of energy, increasing moving away from the nucleus

How are the electrons held within the atom?

By an electrostatic force of attraction towards the positive charge of the protons in the nucleus

What does the atomic number of an element represent?

The number of protons

Can different elements have the same atomic number

No

Therefore…

the no. of protons in an atom (atomic no.) gives identity to the atom

Why is the no. of protons equal to the number of neutrons

because the atom is neutral and has no overall electric charge

In this shorthand notation, which letter represents the atomic number

Z (Z is the symbol given for atomic number)

What is the mass number of an atom

the number of protons and neutrons in the nucleus

in the shorthand notation, which is the symbol for mass number

A

What is the mass number also referred to as

the nucleon number

so the mass number (A) = ….

mass number (A) = number of protons (Z) + number of neutrons (N)

So, if you have the atomic number (no of protons - Z) and you have the mass number (no of protons + neutrons - A), how do you find just the number of neutrons

you subtract the atomic number from the mass number

no of neutrons (N) = mass number (A) - atomic number (Z)

And how would you find the number of electrons in an atom?

The number of electrons is equal to the number of electrons

so whatever the atomic number is, the electron number is

Electrons are arranged in sets of ____ or ____

energy levels or shells

These shells can accept

a limited number of electrons

The first shell can take

up to 2 electrons

The second shell can take

up to 8 electrons

The third shell can take

up to 8 electrons

The way electrons are arranged in an atom is called the

electron configuration (or electron structure)

so lets take carbon as an example, its atomic number is 6 - find its electron configuration

6 protons = 6 electrons

2, 4

The horizontal rows in the periodic table are known as

periods

what does the period number tell us

the number of shells present in an atom

examples?

period 1 - hydrogen and helium = 1 electron shell

period 2 - lithium, neon.. = 2 electron shells

period 3 - sodium, argon.. = 3 electron shells

the vertical columns are known as

groups

elements in the same group have the same

number of electrons in their outer shell

explain

All elements in group 1 have 1 electron in their outermost shell

All elements in group 2 have 2 electrons in their outermost shell

….

What about noble gases

Noble gases, found in group 8 or 0 have a full outer shell (2 or 8)

Sine elements in the same group have the same number of electrons in their outer shell

they have similar chemical properties

What about hydrogen, does it share the same properties as the group 1 elements

No, it does not - ideally hydrogen should be placed on its own

What are isotopes

Isotopes are atoms of the same element with the same number of protons, but different number of neutrons

so in some elements the atoms are not identical

yes

What is the same about isotopes and what is different

• Isotopes have the same chemical properties because they have the same electronic structure/ configuration

• Isotopes have different physical properties (e.g. density) due to more or less neutrons

Why are some isotopes of certain atoms unstable/ said to be radioactive

because of the extra number of neutrons

How were isotopes discovered

using a mass spectrometer

What does the detector in this instrument measure

how many isotopes are present and also the percentage abundance

What is the relative abundance of an isotope

the proportion of one particular isotope in a mixture of isotopes found in nature

e.g. 75% of chlorine atoms are Cl-35 while 25% are Cl-37

The average mass of a large number of atoms of an element is called the

Relative atomic mass (RAM or A_r)

What does this quantity consider

the percentage abundance of all the isotopes of an element which exist

Define RAM

Relative atomic mass is defined as the average mass of isotopes of an element compared to
1/12 th of the mass of an atom of ¹²C

Formula for RAM

When actually working out the RAM, why is there no need to put the bottom part of the formula

because 1/12th of the mass of 1 carbon-12 atom = 1 amu

For compound what two terms are used

Relative molecular mass (RMM)

Relative formula mass (RFM)

Which is used for what?

Relative molecular mass (RMM) - Covalently bonded substances (non-metals)

Relative formula mass (RFM) - Ionically bonded substances (metals and non-metals)

Why do RAM, RMM and RFM have no units

because they are a comparison of masses

DO PRACTICE PROBLEMS!!

yes sir 😉