Atoms Worksheet: Where we are at.• Atom diagrams.

• Protons and neutrons located in the nucleus with surrounding electrons located in discreet energy levels or shells.

Review exercise 3.1• In review exercise 3.1 we used the atomic number

(Z) and the mass number (A) to work out how many protons, neutrons and electrons in neutral atoms.

• Note: Elements are arranged in the periodic table according to their atomic numbers (Z)

Definitions: You need to know these!!!

• Atomic number (Z) = number of protons in the atom.

• Mass number (A) = number of protons + number of neutrons in the atom.

Isotopes• Isotopes are atoms or the same element that have

different numbers of neutrons in the nucleus.• As such their atomic numbers are the same but their

mass numbers differ.Example Question:

Relative Atomic Mass• As atoms are too small to be weighed easily. By convention we

use relative atomic masses to compare atoms.• The modern standard atom is Carbon-12 which has a value of 12

Particle Symbol Mass (kg) Relative mass

Charge (C)

Relative Charge

Proton p 1.673 x 10-27 1 1.60 x 10-19 +1

Neutron n 1.675 x 10-27 1 0 0

Electron e 9.110 x 10-31 ~ 1/1840 1.60 x 10-19 -1

Practice Sheet: Isotopes and relative atomic mass

Activity matching information to elements

Atoms Worksheet

• The other worksheet that you had for homework discussed electron configurations.

• Electron configurations being the arrangement of electrons orbiting the nucleus of an atom.

• Bohr’s work contributed the understanding that electrons are located in energy levels or shells.

Electron Energy Levels• In a neutral atoms the number of electrons is equal to the atomic

number of the atom.• Electrons fill the shells closest to the nucleus first.• The closer to the nucleus a shell is, the lower its energy level. The

shell closest to the nucleus can hold a maximum of two electrons. The second shell out from the nucleus can hold a maximum of eight electrons.

• The maximum number of electrons in each shell is determined by the formula: 2n2

Energy level (n) Energy level symbol Max number of electrons

1 K 2

2 L 8

3 M 18

4 N 32

Question 4

• Question 4 of the worksheet asked you to:-Draw an atom of the elements from atomic number 1 to 20- Answer some questions

Did anyone do this?????• Use the diagrams on the next slide to do this

activity

Trends in electron configurations• From this exercise we see the electrons filling the lowest

shells first. (K, Ca in row three is an exception to this trend)

Electron Configurations• Elements in row 1 going across the table

have electrons in shell 1. Elements in row 2 have electrons in shell 2 etc.

• Also we see that elements in the same group (going down the table) have the same amount of electrons in their outer valence shells.

•Medeleev’s periodic table 1869

http://www.youtube.com/watch?v=nsbXp64YPRQ

What elements are missing from Mendeleev’s table?

Why did Mendeleev’s table not include the Noble gases.

• The noble gases located in group 8 of the periodic table are extremely stable un-reactive elements.

• As such they were not discovered until 1895 by Lord Rayleigh and William Ramsay

Intro to noble gases: http://www.youtube.com/watch?v=QLrofyj6a2s

Nobel gas song: http://www.youtube.com/watch?v=5KiTu4dWXik

Chemical reactivity of the elements.

• Whereas the unreactive nature of the noble gases delayed their discovery, for other elements such as gold the very same reason has meant that thi metal has been known and used since 6000 BC

• Read 2.2 Jacaranda and do questions on page 48• Look at

http://www.periodicvideos.com/videos/079.htm • Reactivity of Rubidium:• http://www.youtube.com/watch?v=m55kgyApYr

Y

Noble gases and the reactivity of elements

• The reluctance of the noble gases to react chemically is the key that unlocks our understanding of why other elements do react.

• Unreactive Species: If an atom has the electron configuration of a

noble gas it will be chemically unreactive, or only react with difficulty.

• Reactive Species: If an atom does not have the same electron

configuration as a noble gas, it will tend to react in order to achieve this.

 • The noble gases are unreactive, because their outer electron shells

are full. A full shell of outer electrons is a particularly stable arrangement. This means that noble gas atoms neither gain nor lose electrons easily; they react with other atoms with great difficulty, or not at all.

Formation and naming of simple ions

Nobel gas song: http://www.youtube.com/watch?v=5KiTu4dWXik

• http://www.youtube.com/watch?v=CV53wfl-oV8 10 min

• Worksheet: Electron configuration and valency

Charge on ions and common polyatomic ions.

• Read p 18-19 surfing scientist• Students to answer the questions

Ionic and Covalent bonds