Atoms - Chemistry Grade 9 - PDF

Atoms Chemistry grade 9 Topic 2 Teacher: Noor Amara & Bader Alsaidi 1 Objectives: Atoms definition. Atomic theory. Subatomic particles. Isotopes definition. Uses of radioactivity. Electron arrangement and configuration....

Atoms Chemistry grade 9 Topic 2 Teacher: Noor Amara & Bader Alsaidi 1 Objectives: Atoms definition. Atomic theory. Subatomic particles. Isotopes definition. Uses of radioactivity. Electron arrangement and configuration. 2  Atoms and Molecules The basic building blocks of everything that we see in the Universe are atoms. The word ‘atom’ basically means ‘indivisible’. Combinations of atoms are called molecules. For example: O2 - a molecule of oxygen H2O - a molecule of water  Elements, mixtures and compounds An element consists of one type of Cu atom only that cannot be divided Cu into simpler substances by chemical methods, all the atoms of Cu an element contain the same Cu number of protons. Cu For example, pure copper consists of copper atoms only.  Elements, mixtures and compounds S Fe Fe A mixture consists of different S types of atoms that are not chemically bonded. S S Fe 1. Particles in a mixture can all be separated out quite easily. 2. No chemical bonds exist 3. Properties of the mixture are just a mixture of the properties of the separated parts.  Elements, mixtures and compounds S Fe In a compound the particles are Fe held together by strong forces S called chemical bonds. A chemical reaction will have taken place. C O O 1. Particles in a compound are very difficult to separate. 2. The properties of a compound are very different to the properties of the original elements. 3. What is the difference between molecules and compounds? https://www.youtube.com/watch?v=0gsrW0Vb5sw  The size of an atom This is the head of a pin. Millions of atoms would fit onto it. So, atoms are very, very, small! An atom is the smallest particle of an element that can exist.  HISTOR Y OF THE ATOM 1808 John Dalton p.36 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS 9  HISTOR Y OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON 10  HISTOR Y OF THE ATOM 1910 Ernest Rutherford Calculated that an atom is mostly space occupied by the negatively charged electrons, surrounding a very small, positively charged nucleus. 11 THE ATOM THE ATOM THE NUCLEUS THE ATOM THE NUCLEUS middle of the atom contains protons and neutrons positive charge (protons are positive) almost all atom mass is concentrated in the nucleus tiny compared to the atom as a whole THE ATOM THE ELECTRONS THE ATOM THE ELECTRONS move around the nucleus in orbits Negatively charged tiny, but cover a lot of space virtually no mass FACTS ABOUT THE ATOM!  FACTS ABOUT THE ATOM! 1. NEUTRAL ATOMS HAVE NO CHARGE OVERALL 2. CHARGE ON THE ELECTRONS IS THE SAME SIZE AS THE CHARGE ON THE PROTONS BUT OPPOSITE 3. IN A NEUTRAL ATOM THE NUMBER OF ELECTRONS EQUALS THE NUMBER OF PROTONS 4. ELECTRONS MAY BE LOST OR GAINED. THE ATOM THEN BECOMES CHARGED, AND IS KNOWN AS AN ION 5. NEUTRON NUMBER S ARE USUALLY JUST A BIT HIGHER THAN PROTON NUMBER S, BUT CAN CHANGE  Facts About Subatomic particles! Particle Mass Charge Proton 1 +1 Neutron 1 0 Electron 1/1840 -1 Atomic Mass and Mass Number 23 11 Na Symbol for sodium  Atomic Mass and Mass Number MASS NUMBER = total number of protons and neutrons 23 11 Na  Atomic Number and Mass Number MASS NUMBER = total number of protons and neutrons 23 ATOMIC NUMBER 11 Na = number of protons (also electrons)  Atomic Mass and Mass Number MASS NUMBER = total number of protons and neutrons 23 ATOMIC NUMBER 11 Na = number of protons (also electrons) Number of neutrons = mass number – atomic number  Atomic Number and Mass Number MASS NUMBER = total number of protons and neutrons 23 ATOMIC NUMBER 11 Na = number of protons (also electrons) Mass number is always bigger than the atomic number  Atomic Mass and Mass Number MASS NUMBER = total number of protons and neutrons 23 ATOMIC NUMBER 11 Na = number of protons (also electrons) For sodium: protons = 11, electrons = 11, neutrons = 12  Atomic Mass and Mass Number Species Atomic number Mass number Protons Neutrons Electrons 6 12 C 9 19 - F 20 40 Ca2+ 11 23 Na 19 39 K+ 17 35 Cl- 13 27 Al 12 24 Mg2+ 8 16 O2- 15 31 3- P 44 101 Ru3+ 14 28 Si 16 32 2- S 80 200 Hg2+  What is an isotope? Watch this video and answer the following questions: https://www.youtube.com/watch?v=SdhLTfma_Eg Define what is meant by relative atomic mass. Calculate the relative atomic mass for the elements given in the video.  What is an isotope? ISOTOPES ARE: different atomic forms of the same element, having the same number of PROTONS but different numbers of NEUTRONS FOR EXAMPLE, there are two common forms of carbon: Carbon 12 Carbon 14 12 14 6 C Protons = 6 6 C Protons = 6 Neutrons = 6 Neutrons = 8 Electrons = 6 Electrons = 6 Chemical properties are the same because the different number of neutrons in the nucleus doesn’t affect the chemical behaviour at all.  What is RELATIVE ATOMIC MASS? By definition: “the average mass of naturally occurring atoms of an element on a scale where the carbon-12 atom has a mass of exactly 12 units” Relative atomic mass is also the same as the mass number – it’s that simple! So why most relative atomic masses are not whole numbers? Why has chlorine got a relative atomic mass (or mass number) of 35.5?  What is RELATIVE ATOMIC MASS? It’s because chlorine has two common isotopes (remember those?) 35 37 Cl 17 AND Cl 17 They are found naturally in the ratio 3:1 So the average relative atomic mass = 35 + 35 + 35 + 37 = 35.5 4 35. So chlorine is written as: 5 17 Cl  What is RELATIVE ATOMIC MASS? Consider the relative abundance of the isotopes of element X Isotope Abundance % 24 X 80 25 X 10 26 X 10 Calculate the relative atomic mass for X.  What is RELATIVE ATOMIC MASS? A sample of iron has the following isotopic composition by mass. Isotope Abundance % 54 Fe 5.95 56 Fe 91.88 57 Fe 2.17 Calculate the relative atomic mass of iron based on this data, giving your answer to two decimal places.  What is RELATIVE ATOMIC MASS? Antimony contains two stable isotopes, 121Sb and 123Sb. The relative atomic mass for antimony is 121.76. Calculate the percentage for each isotope in pure antimony. State your answer to two decimal places. What is RELATIVE ATOMIC MASS? Radioactivity What is radioactive decay? This occurs when an unstable atomic nucleus changes into another nucleus by emitting one or more particles and heat energy. The extra neutrons lead to spontaneous disintegration. Radioactive decay is a nuclear process and not a chemical reaction. https://www.youtube.com/watch?v=UYvx0O8itMA  Uses of radioactive decay 1. Industrial uses: Nuclear power stations Monitoring the level of filling in containers Checking the thickness of sheets Detecting leaks in gas or oil pipes 2. Medical uses: Detection of cancer and killing of cancer cells using coblat-60 to stop the growth of brain tumors Sterilization The radiation kills bacteria, 3. Radioactive dating Uranium is still found in nature because of how long it takes to decay Half-life is the time it takes for a sample of radioactive isotope to decay to half its original mass EXAMPLES: – Uranium-235 takes 713 million years  HISTOR Y OF THE ATOM 1913 Niels Bohr studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons. 39  Bohr’s theory 1. Electrons are in orbit around the central nucleus of the atom. 2. The electron orbits are called shells (or energy levels) and have different energies. 3. Shells which are further from the nucleus have higher energies. 4. The shells are filled starting with the one with the lowest energy (closest to the nucleus). 5. The first shell can hold only 2 electrons. 6. The second and subsequent shells can hold 8 electrons to give a stable (noble gas) arrangement of electrons. Exercise Work out the electron configuration with the drawing in rings for the first 20 elements in the periodic table. https://www.youtube.com/watch?v=hSkJzE2 Vz_w