AQA Additional Science Chemistry 2 Lesson 3.1 Mass number

Aims Class work 6 September 2007 Mass Number LO’s What is the mass number? What’s an isotope? Write it down!! Page 50 © C Meyer

Chemistry Unit 2 Sections Structures Structures and bonding  and properties  How much? 3 of 7 © C Meyer

Aims All Know the relative masses of sub atomic particles Know what an isotope is Most Work out the mass number of an atom Some Explain how isotopes are different

What have I learnt? T/F Quiz – Back Atoms are charged particles Electrons are found in energy levels Electrons are found in shells Electrons have a negative charge Protons are in the nucleus of the atom Neutrons are found in shells around the nucleus The atomic number is the number of protons

What have I learnt? What does the structure of the atom look like? There are two properties of sub-atomic particles that are especially important: Electrical charge (looked at before) Mass (Need to look at now) Charge Particle -1 Electrons Neutrons +1 Protons Overall neutral Particle Charge Relative Mass Protons +1 1 Neutrons Electrons -1 0.0005 Mass of proton = mass of neutron (relative mass = 1) Ignore mass of electron m5

15 Mins

What have I learnt? Atomic/Proton Number The atom of any particular element always contains the same number of protons. E.g. Hydrogen atoms always contain 1 proton Carbon atoms always contain 6 protons Magnesium atoms always contain 12 protons The number of protons in an atom is known as its atomic/proton number. It is the smaller of two numbers shown in most periodic tables 12 C 6

Activity How Many Protons? Here is some data about elements taken from the Periodic Table. What is the atomic number of the elements? 23 Na 11 56 Fe 26 119 Sn 50 19 F 9 27 Al 13 11 26 50 9 13

What have I learnt? How Many Protons? Note elements have a definite and fixed number of protons. Changing number of protons in atom changes that atom into a different element.

What is the mass number? Mass Number – What is it? The mass of each atom comes almost entirely from the number of protons and neutrons that are present. (Remember that electrons have a relatively tiny mass). MASS NUMBER = Number of protons + number of neutrons Atom Protons Neutrons Mass Number Hydrogen 1 Lithium 3 4 7 Aluminium 13 14 27 m2

Activity What is the mass number? In back - Calculate the mass number of the atoms shown. Atom Protons Neutrons Mass Number Helium 2 Copper 29 35 Cobalt 27 32 Iodine 53 74 Germanium 41 4 64 59 127 73 MASS NUMBER = Number of protons + number of neutrons

What is the mass number? Mass number = protons + neutrons It is the bigger of two numbers shown in periodic table 12 C 6 Atomic/proton number = protons. It is the smaller of two numbers shown in periodic table m1

Activity What is the mass number? In back - Calculate the number of neutrons in these atoms. Number of Neutrons = mass number - atomic number Atom Mass Number Atomic Number Number of Neutrons Helium 4 2 Fluorine 19 9 Strontium 88 38 Zirconium 91 40 Uranium 238 92 2 10 50 51 146

What have I learnt? In Front - Copy and fill in the blank columns 5 5 Activity What have I learnt? In Front - Copy and fill in the blank columns Atom Protons Neutrons Electrons Atomic number Mass Number Boron 5 6 Potassium 19 20 Chromium 24 28 Mercury 80 121 Argon 18 22 5 5 11 19 19 39 24 24 52 80 80 201 18 18 40 Note – atomic number is defined as the number of protons rather than electrons because atoms can lose (or gain) electrons but do not normally lose protons

30 Mins

What’s an isotope? Natural samples of elements are often a mixture of isotopes. About 1% of natural carbon is carbon-13. C 13 6 1% C 12 6 99% What’s the difference? 6 6 7 Protons Electrons Neutrons m1

ATOMS are just like the Ford Fiesta What is relative mass? ATOMS are just like the Ford Fiesta ISOTOPE m2

There are different versions of the FIESTA SPEEDY m3

We also have different versions of the same element’s atoms WE CALL THEM ISOTOPES m1

The only difference between the atoms in an isotope is that they contain different numbers of NEUTRONS

Remember: The number of What’s an isotope? It is not strictly true to say that elements consist of one type of atom. Atoms in an element always have the same number of protons but may have different numbers of neutrons. Atoms like this are called isotopes. Remember: The number of protons defines the element

H H H Isotopes: Hydrogen Hydrogen exists as 3 isotopes although Hydrogen-1 makes up the vast majority of the naturally occurring element. All can make water H 1 H 2 1 H 3 1 Protons Electrons Neutrons Hydrogen Protons Electrons Neutrons (Deuterium) Protons Electrons Neutrons (Tritium) m4

Cl Cl Isotopes: Chlorine About 75% of natural chlorine is 35Cl the rest is 37Cl. Cl 35 17 75% Cl 37 17 25% How many neutrons? 17 Protons Electrons Neutrons Protons Electrons Neutrons 17 18 20

Activity Isotopes of Oxygen 16 O 8 Almost all of natural oxygen is 16O but about 0.2% is 18O. Produce a Table showing the particles in each isotope. Oxygen-16 Oxygen-18 Protons Electrons Neutrons 8 Protons Electrons Neutrons 8 8 8 8 10

What’s an isotope? Isotopes are virtually identical in their chemical reactions as have same number of protons and electrons. The uncharged neutrons only affect physical properties such as melting point and density.

What have I learnt? Draw the electronic structure of carbon 12 and carbon 14 Say how many protons, neutron Draw up a table of similar properties and differences Same Different

C What have I learnt? 12 6 99% 13 1% Same Different Protons Electrons Neutrons 6 7 Same Different Same number electrons Different number neutrons Same number protons Different mass number Same chemical properties Different physical props Same proton number

Homework Section 2 test

What have I learnt?

The End