LESSON-2.pptx

LESSON 2: ATOMS, MOLECULES AND IONS JOHN DALTON’S ATOMIC MODEL A theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates: (1) Elements consist of indivisible small particles (atoms). (2) All atoms of the same element are identical; different eleme...

LESSON 2: ATOMS, MOLECULES AND IONS JOHN DALTON’S ATOMIC MODEL A theory of chemical combination, first stated by John Dalton in 1803. It involves the following postulates: (1) Elements consist of indivisible small particles (atoms). (2) All atoms of the same element are identical; different elements have different types of atom. (3) Atoms can neither be created nor destroyed. SCIENTIFIC LAWS The law of conservation of mass states that matter cannot be created or destroyed. The law of definite proportions states that a given chemical compound always contains the same elements in the exact same proportions by mass. The law of multiple proportions states that whenever the same two elements form more than one compound, the different masses of one element that combine with the same THE SUBATOMIC PARTICLES An atom is defined as the smallest unit of an element that still has the properties of that element. Atoms can, in fact, be broken apart into smaller units called subatomic particles. -proton -electron -neutron HISTORY OF ATOMIC STRUCTURE Thomson proposed the plum pudding model of the atom, which had negatively- charged electrons embedded within a positively-charged "soup.“ Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. THOMSON PLUM PUDDING MODEL RUTHERFORD’S GOLD FOIL EXPERIMENT DISCOVERY OF PROTON Eugen Goldstein had observed in 1886 a display of bright rays coming from the positive electrode (anode) of the cathode tune. He noticed that the bright rays moved through the cathode punctured with holes and struck the end of the cathode tube. The bright rays were a stream of positively-charges particles called protons. DISCOVERY OF PROTON  DISCOVERY OF NEUTRON The British physicist Sir James Chadwick discovered neutrons in the year 1932. James Chadwick fired alpha radiation at beryllium sheet from a polonium source. This led to the production of an uncharged, penetrating radiation. This radiation was made incident on paraffin wax, a hydrocarbon having a ATOM, MOLECULES AND IONS Atoms are single neutral particles. Molecules are neutral particles made of two or more atoms bonded together. An ion is a positively or negatively charged particle.  ATOMIC NUMBER & MASS NUMBER The atomic number of an atom is the number of protons in its nucleus. Atomic number = # of protons= # of electrons The mass number of an atom is the sum of number of protons and neutrons in its nucleus. Mass number = # of protons + # of neutrons Number of neutrons = mass number - # of protons  Mass number and atomic number sample elements. Eleme Mass Atomi No. Of No. Of No. Of nt numbe c Proton Electr Neutro r numbe s ons ns r O 16 8 8 8 8 Si 28 14 14 14 14 N 14 7 7 7 7  Activity: Complete the table Element Mass Atomic No. Of No. Of No. Of number number Protons Electron Neutron s s 32 43 55 25 108 47 14 14 S