Chapter 2: The STRUCTURE of the ATOM

Learning outcomes:

Sub-atomic particles (protons, neutrons and electrons), Isotopes

Structure of the atom

Behavior of sub-atomic particles in electric fields

English check Atom Molecule Proton Neutron Electron Isotope Electric field Positive charge Negative charge Nucleus

Deflection Positive ion Negative ion Beam Periodic table of elements Nucleon Relative atomic mass Subatomic particle

Check Deflection Positive ion Negative ion Beam Periodic table of elements Nucleon number Mass number Atom number Relative atomic mass

proton

neutron

electron

Since 1932 we know that atoms are made from smaller subatomic particles. There are three types of subatomic particles:

Inside the Atom: a labelled diagram of the atom with: the nucleus, protons, neutrons and electrons.

nucleus

neutron proton

electron

Which element does this diagram represent?

Particle SymbolRelative

massRelative charge

electron e 0 -1

neutron n 1 0

proton p 1 +1

How do we know the charge of subatomic particles?

From experiment to knowledge

Deflection of sub-atomic particles

The behavior of protons, neutrons, and electrons in electric field

Protons are positively charged and so would be deflected on a curving path towards the negative plate.

Electrons are negatively charged and so would be deflected on a curving path towards the positive plate.

Neutrons don't have a charge, and so would continue on in a straight line.

Check!

Example: Boron

B5

10.8

boron

From the table of elements we can not see how many isotopes an element has Symbol of the

element

Name of the element

Proton or atomic number

Relative atomic number (Ar)

Boron has 2 isotopes

5B

5B

10

11

Question: how many % of the boron atoms is B-10 and how many % is B-11?

“Boron-10” or

“Boron-11” or

Atomic- and mass number

Proton- or Atomic number (Z) is the number of protons in the nucleus of an atom

Nucleon- or Mass number (A) is the sum of protons and neutrons in the nucleus of an atom.

ZX with X the symbol for the element.

e.g. 4Be, 6C, 12Mg

A

9 12 24

Number of protons = Z

Number of neutrons =

Number of electrons = Z or >Z or <Z

How many??

Number of protons + neurons = A

A - Z

For “ion” the number of proton is NOT the same as electrons

Find the number of protons, neutrons and electrons in each of these neutral elements:

Find the number of protons, neutrons and electrons in each of these ions:

12Mg2+11Na+

17Cl-

O2-

24 23 1635

Isotopes

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

17Cl and 17Cl

Smart instrument

35 37

We can now determine the “relative atomic mass” of the Cl-atom

Isotopes

The hydrogen atom has 3 isotopes

Isotopes

Which one of these statements best describes isotopes? A Atoms of the same element with different numbers of neutrons B Atoms of different elements with different numbers of nucleons C Atoms of the same element with different numbers of electrons D Atoms of different elements with the same number of nucleons

Elements: which can not be broken down further into simpler substances by chemical means. Or contain only one type of atom.

A tiny region in the center of the atom is called nucleus (pl. nuclei)

Proton: a subatomic particle with a relative mass of 1 and a charge +1 found in the nucleus of all atoms.

Neutron: an uncharged subatomic particle present in the nuclei of atoms – a neutron has a mass of 1 relative to a proton.

Vocabulary

Vocabulary Electron: a subatomic particle with negligible mass

and a charge of -1. The nucleus is made up of particles called nucleons

(protons and neutrons) Each shell is a certain distance from the nucleus at its

own particular energy level.