1. Proton, Electron & Neutron Numbers Noadswood Science, 2011

2. Proton, Electron & Neutron Numbers To know the structure of an atom and be able to work out proton, electron and neutron numbers Saturday, October 01, 2016 Electrons Nucleus containing protons and neutrons

3. Atoms – Early Ideas The word atom comes from atomos, an ancient Greek word meaning indivisible: the Greek philosopher Demokritos (460- 370 BCE) maintained that all matter could be divided and sub-divided into smaller and smaller units, and eventually there would be a tiny particle that could not be divided any further - an atom Understanding of atoms didn’t progress much beyond Demokritos’ theory until the English chemist John Dalton (1766 - 1844) started to look at it in the 1800s…

4. Atoms – Early Ideas Dalton came to the following conclusions: - All matter is made of atoms, and atoms are indestructible and cannot be broken down into pieces All the atoms of a particular element are identical to each other and different from the atoms of other elements Atoms are rearranged in a chemical reaction Compounds are formed when two or more different kinds of atoms join together

5. Atoms How can we represent an atom? What does an atom contain? Atoms have a small central nucleus (containing protons and neutrons) which is orbited by electrons All substances are made from atoms, and any given element is made of atoms of just one particular sort – represented by a specific chemical symbol

6. Atom Structure The nucleus: - In the middle of the atom Contains protons and neutrons Has a positive (+ve) charge (due to the presence of the protons) Almost the whole mass of the atom is concentrated within the nucleus Size is tiny compared to the atom as a whole! The electrons: - Orbit the nucleus Negatively charged (-ve) Tiny, but cover a lot of space The volume of their orbits determines how big the atom is Virtually no mass They occupy shells around the nucleus Electrons Nucleus containing protons and neutrons ParticleMassCharge Proton1+1 Neutron10 Electron1/2000

7. Protons & Electrons Neutral atoms have no overall charge – the size of the charge of the electrons is the same as that of the protons, just opposite (electrons are –ve and protons are +ve) This means in an atom the number of protons equals the number of electrons *Electrons can be added / removed – if this is done the charged atom is known as an ion (watch the sweet demo)!

8. Atomic Number & Atomic Mass Periodic table shows one final important piece of information - an element’s atomic number and it’s atomic mass… The mass number (top number) shows the number of protons + neutrons The atomic number (bottom number) shows the number of protons (and therefore, the number of electrons) O Mass number Atomic number O 16 8

9. Atomic Number & Atomic Mass Using the periodic table work out how many neutrons, protons and electrons and found in the following atoms: - Hydrogen Helium Lithium Carbon Oxygen O Protons + neutrons Protons (therefore electrons)

10. Atoms Remember: - The mass number (top number) shows the number of protons + neutrons The atomic number (bottom number) shows the number of protons (and therefore, the number of electrons) Hydrogen: - Mass number 1 (1 proton and 0 neutrons) Atomic number 1 (1 proton & 1 electron) Helium: - Mass number 4 (2 protons and 2 neutrons) Atomic number 2 (2 protons & 2 electrons) O Mass number Atomic number

11. Atoms Lithium: - Mass number 7 (3 protons and 4 neutrons) Atomic number 3 (3 protons & 3 electrons) Carbon: - Mass number 12 (6 protons and 6 neutrons) Atomic number 6 (6 protons and 6 electrons) Oxygen: - Mass number 16 (8 protons and 8 neutrons) Atomic number 8 (8 protons and 8 electrons) O Mass number Atomic number

12. Atomic Mass & Number The periodic table also shows some key information about an element’s atomic mass and atomic number… Atomic mass Number of protons + neutrons Atomic number Number of protons (therefore number of electrons too in a neutral atom) 6 protons 6 neutrons 6 electrons

13. Questions How many protons, neutrons and electrons are there in the following… 1 protons 0 neutrons 1 electrons HBO 1 1 11 5 16 8 5 protons 6 neutrons 5 electrons 8 protons 8 neutrons 8 electrons

14. Questions How many protons, neutrons and electrons are there in the following… NaClU 23 11 35 17 238 92 11 protons 12 neutrons 11 electrons 17 protons 18 neutrons 17 electrons 92 protons 146 neutrons 92 electrons

15. Atomic Discoveries

16. Theories A theory is a suggestions which could explain why something is happening or why something is observed – it is not a guess or a fact Theories can be changed if better evidence is available For example the greenhouse effect is a theory about why global warming is occurring (but there are other theories)! These apples keep falling to the ground - perhaps there is a force pulling them (gravity)?!