Atoms T. M. Yeung 2000

w What is the particle that made up an element?

Atoms w All elements are made up of small particles called atoms. w Different elements have their unique kind of atoms. w The atoms of iron are different from that of carbon.

Gold and its Atoms

Different Elements are made up of different atoms a silver wire silver atoms enlarged many, many times a copper wire copper atoms enlarged many, many times

Basic Structure of Atom

Solar System

Basic Structure of Atom

Atomic Number & Mass Number w An Atom is electrically neutral, that means w No. of proton(s) in an atom = No. of electron(s) in the same atom w Atomic Number (Z) of an atom = No. of proton(s) of the atom w Mass Number (A) of an atom = No. of proton(s) + No. of neutron(s)

Example w What is the atomic number and the mass number of the atom shown below? neutron electron proton nucleus Atomic number is 2 and mass number is 4

Class-work

Notation of Atom w X = symbol of element w Z = atomic number w A = mass number

Notation of Atom w Atomic no. =? w 92 w Mass no. =? w 235 w No. of the neutron =? w 143 w Name =? w Uranium

Atomic Bombing at Nagasaki

Class-work

Isotopes of Hydrogen

Chemistry Dictation w First 20 elements w 10 minutes:

Relative Atomic Mass w The mass of a hydrogen atom is only 1.66 x g! w The mass of a carbon atom is only 2 x g! ( g!) w Carbon-12 atom is being taken as the reference standard. w The relative atomic mass of carbon-12 atom is defined as 12 units.

w Most elements have more than one isotope, and different isotopes have different masses. w The relative atomic mass of an element is the average mass of its isotopes compare with an atom carbon-12. Relative Atomic Mass

w IsotopePercentage abundance 35 Cl75% 37 Cl25% w Relative atomic mass of chlorine, Cl: 75/100 x /100 x 37 = 35.5 (a.m.u.) # w Relative atomic mass of lead, Pb: 2/100 x /100 x /100 x /100 x 208 = (a.m.u.) #

Electron Arrangement of Atoms nucleus

Electron Arrangement of Atoms w Oxygen atom w Atomic no. = 8 w No. of protons = No. of electrons = 8 w Electron arrangement = 2, 6 O Electron

Electron Arrangement of Atoms w Oxygen atom w Atomic no. = 8 w No. of protons = No. of electrons = 8 w Electron arrangement = 2, 6 Electron O

Electron Arrangement of Atoms w Oxygen atom w Atomic no. = 8 w No. of protons = No. of electrons = 8 w Electron arrangement = 2, 6 O Electron

Electron Arrangement of Atoms w Oxygen atom w Atomic no. = 8 w No. of protons = No. of electrons = 8 w Electron arrangement = 2, 6 O Electron

Electron Diagram of Oxygen Atom O electron w Two electrons in the first shell. w Six electrons in the second shell. w Electron arrangement = 2, 6

Electron Diagram of Aluminium Atom w Atomic no. = 13 w Electron arrangement =2, 8, 3 w Two electrons in the first shell. w Eight electrons in the second shell. w Three electrons in the third shell Al

Electron Diagram of Magnesium Atom w Atomic no. = 12 w Electron arrangement = 2, 8, 2 Mg

Electron Diagram of Fluorine Atom w Atomic no. = 9 w Electron arrangement = 2, 7 F

Electron Diagram of Boron Atom w Atomic no. = 5 w Electron arrangement = 2, 3 B

Simple Ions w A simple ion is formed when an atom either loses or gains one or more electrons. w It is either positively or negatively charged. w Positive ions are called cations.

Simple Ion

Simple Ion: Cation w Lithium atom, Li: w Atomic no. = 3 w Electron arrangement = 2, 1 w Remove one electron from the outermost shell of lithium atom... Li

Simple Ion: Cation w Lithium ion, Li + : w Atomic no. = 3 w Electron arrangement = 2 w Three protons w Two electrons w Positively charged particle! Li +

Simple Ion: Anion w Fluorine atom, F: w Atomic no. = 9 w Electron arrangement = 2, 7 w Add one electron to the outermost shell of fluorine atom... F

Simple Ion: Anion w Fluoride ion, F - : w Atomic no. = 9 w Electron arrangement = 2, 8 w Nine protons w Ten electrons w Negatively charged particle F -

References w Atomic Bomb ndex1.html w Encarta 98 w General Chemistry wilson.ucsd.edu/education/gchem/index.html w General Chemistry I -- A Virtual Textbook