GED compounds to understand atom and elements (refer general chemistry).pptx

To understand atom and elements, refers (general chemistry

1. Atoms and Elements Dr Aung

2. 3.1 3.2 3.3 3.4 3.5

3. Atoms and elements 3.1 Atoms are the smallest particles of matter, that we cannot break down further by chemical means . + - Nucleus = P + + n P + = protons n = neutrons e - = electron Empty space In fact atoms are mostly empty space . Each consists of a nucleus and a cloud of particles called electrons that whizz around it.

4. The elements Sodium is made of sodium atoms only, so it is an element. An element contains only one kind of atom . Around 90 elements have been found in the Earth and atmosphere. Scientists have made nearly 30 others in the lab. Many of the ‘artificial’ elements are very unstable, and last just a few seconds before breaking down into other elements. (That is why they are not found in nature.)

5. The periodic table

6. It gives the names and symbols for the elements. The vertical column is called groups, same groups have similar chemical properties. The horizontal row is called period, same period have same number of shell. Zig-zag line separates metals from non metals.

7. More about atoms 3.2 Protons, neutrons, and electrons Atoms consist of a nucleus and a cloud of electrons that move around the nucleus. The nucleus is itself a cluster of two kinds of particles, protons and neutrons. All the particles in an atom are very light . So their mass is measured in atomic mass units (amu) , rather than grams. Protons and electrons also have an electric charge. Since electrons are so light, their mass is usually taken as zero. 1/1840 amu

8. The number of protons in an atom is called its proton number . Every atom has an equal number of protons and electrons. So atoms have no overall charge . The total number of protons and neutrons in an atom is called its nucleon number.

9. Isotopes and radioactivity 3.3 Isotopes All carbon atoms have 6 protons. But not all carbon atoms are identical. Some have more neutrons than others. Isotopes are atoms of the same element, with different numbers of neutrons . Most elements have isotopes. For example calcium has six, magnesium has three, iron has four, and chlorine has two.

10. Some isotopes are radioactive A carbon-14 atom behaves in a strange way. It is radioactive . That means its nucleus is unstable . Sooner or later the atom breaks down naturally or decays , giving out radiation in the form of rays and particles, plus a large amount of energy . Like carbon, a number of other elements have radioactive isotopes – or radioisotopes – that occur naturally, and eventually decay. But the other two isotopes of carbon (like most natural isotopes) are non-radioactive.

11. Radiation can harm you If the radiation from radioisotopes gets into your body, it will kill body cells. A large dose causes radiation sickness. Victims vomit a lot, and feel really tired. Their hair falls out, their gums bleed, and they die within weeks. Even small doses of radiation, over a long period, will cause cancer. Making use of radioisotopes To check for leaks: Engineers can check oil and gas pipes for leaks by adding radioisotopes to the oil or gas. If a Geiger counter detects radiation outside the pipe, it means there is a leak. Radioisotopes used in this way are called tracers. To treat cancer : Radioisotopes can cause cancer. But they are also used in radiotherapy to cure cancer To kill germs and bacteria :

12. How electrons are arranged 3.4 Electron shells (K.L.M.N….) Electrons are arranged in shells around the nucleus. The first shell, closest to the nucleus, is the lowest energy level . The further a shell is from the nucleus, the higher the energy level. Each shell can hold only a certain number of electrons . (2n 2 )

13. Pattern in Periodic Table The period number tells you how many shells there are. All the elements in a group have the same number of electrons in their outer shells. So Group I elements have 1, Group II have 2 and so on. These outer shells electrons are also called the valency electrons. The group number is the same as the number of outer shell electrons, except fore Group 0. The valency electrons dictate how an element reacts. So the elements in Group I all have similar reactions.

14. The elements after calcium Example The element rubidium, Rb, is the 37th element in the Periodic Table. It is in Group I, Period 5. Its proton number is 37. What is its electron distribution ? Group I tells you there is 1 electron in the outer shell. Period 5 tells you there are five shells. The proton number is 37 , so there are also 37 electrons. The third shell holds 18 electrons, when full. So the electron distribution for rubidium is: 2.8.18.8.1 Rb 37 85

15. The metals and non-metals The zig-zag line separates the elements into two groups: metals and non-metals. The non-metals lie to the right of the line, except for hydrogen. there are many more metals than non-metals. In fact over 80% of the known elements are metals.

16. Chemical properties Physical properties

17. Exceptions to those properties not all metals are hard solids. You can cut sodium and potassium with a knife, and mercury is a liquid at room temperature. https://www.youtube.com/watch?v=AaNp50JgaK0 hydrogen is a non-metal, but forms positive ions (H + ) like metals do. https://www.youtube.com/watch?v=dpV8Ez02p0U carbon is a non-metal, but one form of it (graphite) is a good conductor; another form (diamond) is very hard, with a very high melting point.

18. Making use of the metals Because metals are generally hard and strong, and good conductors, we make great use of them. For example: Iron is the most-used metal in the world. It is used in buildings, bridges, cars, tin cans (coated with tin), needles, and nails. Copper is used for electrical wiring in homes. Aluminium is strong but light. So it is used in planes and space rockets.

19. Non-metals are everywhere There are far fewer non-metals than metals. But they are all around us – and inside us. Air is almost 80% nitrogen, and about 20% oxygen. Water is a compound of hydrogen and oxygen. Our bodies are mostly water, plus hundreds of carbon compounds. Many of these contain atoms of other non-metals too, such as nitrogen, phosphorus, and iodine. (Plus metals such as calcium and iron.) Sand is mainly the compound silicon dioxide, formed from silicon and oxygen.