- Matter is composed of particles called atoms and molecules. Atoms are the smallest particles that make up elements, and molecules are made of two or more bonded atoms. - The structure of the atom has been discovered over time by scientists like Dalton, Thomson, Rutherford, Bohr, and Chadwick. We now know atoms have a tiny, dense nucleus containing protons and neutrons, surrounded by electrons. - Isotopes are atoms of the same element with different numbers of neutrons. Some isotopes are unstable and radioactive, while others are stable. Radioactive isotopes have important applications in medicine, agriculture, and industry.

2. Particulate Nature of Matter Matter- anything that has mass and occupies space Particle + particle = matter Iron (Fe) from iron atom NaCl from sodium ions and chloride ion H2O from water molecules

3. Atoms an atom is the smallest particle of an element example : “O” for oxygen atom Molecules contains two or more atoms which are bonded together ( maybe same element or not ) example : H2 and CCl4 Ions -ions are charged either positive or negative -are form in liquid or molten state -lose electron (+ ion),gain electron (- ion) example : Na + , Mg 2+ , Br -

4. Kinetic Theory of Matter Solids - strong forces of attraction - particle only vibrate (fixed shape and volume) Liquids - force of attraction weak than solid - particle can move around (follow container shape) Gases - no attraction between particles - particle move faster and freely (zigzag)

6. Diffusion - example : perfume - light and small particle diffuse faster - heavy and large particle diffuse slow

8. The Atomic Structure Democritus Democritus proposed that if a piece of gold cut into smaller until cannot cut anymore, called atom. John Dalton (1766-1844) J.J.Thomson (1856-1940) Ernest Rutherford (1871-1937) Neils Bohr (1885-1962) James Chadwick (1891-1974)

9. John Dalton(1766-1844) In 1808, he proposed : All matter is composed of atoms. Atoms cannot be created or destroyed. All the atoms of an element are identical. The atoms of different elements are different. When chemical reactions take place, atoms of different elements join together to form compounds.

10. J.J.Thomson (1856-1940) It was the first model of the atom. 1897- Thomson discovered the electron (negatively- charged). Thomson suggested that an atom is a positively- charged sphere with electrons embedded in it like a raisin pudding.

11. Ernest Rutherford (1871-1937) 1914- Rutherford discovered the proton Rutherford model was based on the alpha particle scattering experiment He proposed 1) all the positive charge of an atom is concentrated in the nucleus 2) an atom consists of a positively-charged nucleus with a cloud of electrons surrounding the nucleus

12. Neils Bohr (1885-1962) He was a student of Rutherford He proposed 1) electrons are arranged in orbits (electron shells) around the nucleus of the atom 2) electrons in a particular path have a fixed energy. To move from one orbit to another, an electron must gain or lose the right amount of energy

13. James Chadwick (1891-1974) He proposed that the nucleus of the atom contains proton and neutron and the nucleus is surrounded by a cloud of electrons

14. Proton number and nucleon number Proton number = the number of protons in an atom Also known atomic number No two different element have same proton number Atom are neutral. Proton number also tells us number of electron. Nucleon number also known mass number Nucleon no. = proton no. + neutron number How nucleon no. and proton no. of an element is written ?

15. Symbol of elements Most symbols are taken from the English name H C N B Element Symbol Hydrogen Carbon Nitrogen Boron

16. Some symbol are made up of two letters Some symbols are based on the Latin or Greek name Zinc Zn Aluminium Al Calcium Ca silicon Si Silver Ag Copper Cu Iron Fe Gold Au

17. Isotopes and their importance Are atoms of the same element with the same proton no. but different nucleon no. or neutron no. Isotopes of an element have same chemical properties but different physical properties Example of isotopes Some isotopes are stable while the rest unstable ( radioactive isotopes)

18. Uses of isotopes Medicine Cobalt-60 is a radioactive isotope of cobalt. It decays by giving out gamma radiation. In radiotherapy, maglinant cancer cells are killed by directing a beam of gamma rays towards cancer cells Agriculture radiation from radioisotopes is used to sterilise pests such as insects that destroy crops. Industry Gamma radiation is used to detect whether canned food or bottled drink is completely or partially filled

19. Electronic structure of an Atom The electron in atom are arranged in shell around its nucleus Electron start to fill up the shells from the inner shells The first shell is the shell that nearest to nucleus and can hold just 2 electrons Second shell can hold 8 electrons Third shell can hold 8 electrons All of this is called the electron arrangement or electronic configuration of the atom Draw electronic arrangement if proton number is 4,5 and 6

20. Valence electrons Outermost shell of an atom is called the valence shell This shell should have electrons before it can be called a valence shell The electrons in the valence shell are called the valence electrons Elements with the same number of valence electrons have the same chemical properties Lets see the example susunan elektron.swf