Starter On MWB: Draw and label a diagram of an atom of helium with its sub-atomic particles (with relative masses and charges)

Learning outcomes: Define the terms mass number and atomic number (Grade C) Define an isotope and give examples (Grade B) Explain why the isotopes of the same element have identical chemical properties (Grade A) Specification reference 3.1.1

Atomic number, Z Atoms consist of a tiny nucleus made up of protons and neutrons. This nucleus is surrounded by electrons. The number of protons in the nucleus is known as the atomic number or the proton number Z. The atomic number defines the chemical identity of the element e.g. All sodium atoms have 11 protons

Mass number, A The total number of protons and neutrons in the nucleus is called the mass number A. It is the nucleons that make up the mass of the atom because electrons weigh virtually nothing. Mass number A = no. protons + no. neutrons

What’s the number?

Isotopes What are isotopes? Isotopes are atoms of the same element that contain different numbers of neutrons. Is the reactivity of an isotope different to another isotope of the same element? The reactivity of different isotopes of an element is identical because they have the same number of electrons Are the physical properties of an isotope different to another isotope of the same element? The different masses of the atoms means that physical properties of isotopes are slightly different.

Isotopes of chlorine About 75% of naturally-occurring chlorine is chlorine-35 ( 35 Cl) and 25% is chlorine-37 ( 37 Cl). 17 protons 18 neutrons 17 electrons 17 protons 20 neutrons 17 electrons

Isotopes of carbon Can you complete the table for the different isotopes of carbon? Carbon-12 Carbon-13 Carbon-14 NeutronsProtonsIsotope Extension – Who was Willard Libby and why is he important? Explain briefly how his technique can be used

Summary questions 1. Isotopes of hydrogen have been given their own names. Hydrogen-2 is known as deuterium and hydrogen-3 tritium. State how many p, n & e the atoms of the following have. a. Deuterium b. Tritium W, 14 7 X, 16 8 Y and 15 7 Z Identify which of these atoms (not their real symbols) is a pair of isotopes. 3. For each element in question 2, state: a. The number of protons b. The mass number c. The number of neutrons

Arrangement of electrons Describe how electrons are arranged in an atom (Grade C) Describe how the structure of an atom developed from Dalton to Schrödinger Recognise that the electron can behave as a particle, a wave, or a cloud of charge

Electron arrangement Read the page on the link attached

Electron shells The electron shell model is still used at A-level particularly for describing the bonding of simple compounds Electron shells First shell holds up to two electrons Second shell up to eight electrons Third shell holds up to eighteen electrons

Electron diagrams Draw the electron arrangement for the following atoms: Carbon Sulfur Sodium Draw the electron arrangement for the following ions: Na + O 2- Mg 2+

Summary questions 1. Draw the electron arrangement diagrams of atoms that have the following numbers of electrons a. 3 b. 9 c State, in shorthand, the electron arrangement of atoms with: a. 4 electrons b. 13 electrons c. 18 electrons

3. Identify which of the following are atoms, positive ions, or negative ions. Give the size of the charge on each ion, including its sign. Use the Periodic Table to identify the elements A-E Number of protons Number of electrons A1210 B22 C1718 D10 E32