This document discusses the structure of atoms and their organization on the periodic table. It describes atoms as being made up of protons, neutrons, and electrons, with protons and neutrons located in the nucleus and electrons surrounding it in an electron cloud. Elements are defined as materials made of only one type of atom, and are organized on the periodic table by their atomic symbols. Isotopes are variants of the same element that differ in the number of neutrons. The document also briefly mentions ions, which form when atoms gain or lose electrons.

1. Atoms on the PeriodicAtoms on the Periodic
TableTable

2. ObjectivesObjectives
1.1. Describe the present model of theDescribe the present model of the
atom explaining electrons, neutrons,atom explaining electrons, neutrons,
and protonsand protons

3. Periodic TablePeriodic Table
Atoms make up all matterAtoms make up all matter
Elements are any material that is made upElements are any material that is made up
of only one type of atomof only one type of atom
Elements are organized onto the periodicElements are organized onto the periodic
tabletable

4. Each element is designated an atomicEach element is designated an atomic
symbol on the periodic tablesymbol on the periodic table

5. AtomsAtoms
Atoms cannot beAtoms cannot be
seen with visible lightseen with visible light
Robert BrownRobert Brown
First to discover directFirst to discover direct
evidence of the atomevidence of the atom

6. An Atom is made up of three parts:An Atom is made up of three parts:

ProtonsProtons

NeutronsNeutrons

ElectronsElectrons

7. ElectronsElectrons
Electrons surround the nucleus in anElectrons surround the nucleus in an
electron cloudelectron cloud
Electrons carry a negative chargeElectrons carry a negative charge
The atom is mostly empty spaceThe atom is mostly empty space

8. Electron Cloud ModelElectron Cloud Model

9. Why don’t we pass through one another?Why don’t we pass through one another?
Electrical repulsion – two electrons withElectrical repulsion – two electrons with
negative charges will repel each othernegative charges will repel each other

10. ProtonsProtons
Protons and neutrons are bound to theProtons and neutrons are bound to the
atomic nucleusatomic nucleus
Protons carry a positive chargeProtons carry a positive charge
Protons are identified byProtons are identified by Atomic numberAtomic number
atom is electrically neutral: Number ofatom is electrically neutral: Number of
protons = number of electrons;protons = number of electrons;

11. NeutronsNeutrons
Neutron has no electrical charge, but theNeutron has no electrical charge, but the
same mass as a protonsame mass as a proton
Protons and neutrons are called nucleonsProtons and neutrons are called nucleons
Mass given to each proton and neutron is 1Mass given to each proton and neutron is 1

12. Atomic MassAtomic Mass
• Electrons are so small they areElectrons are so small they are
considered negligible in massconsidered negligible in mass
• Atomic mass is measured in the unit –Atomic mass is measured in the unit –
amuamu

Atomic Mass UnitAtomic Mass Unit
Atomic mass on the periodic tableAtomic mass on the periodic table

13. Isotopes and Ions
March 10, 2015

14. Electrons are so small they areElectrons are so small they are
considered negligible in massconsidered negligible in mass
Protons and neutrons in the nucleusProtons and neutrons in the nucleus
• Atomic mass is measured in the unit –Atomic mass is measured in the unit –
amuamu

Atomic Mass UnitAtomic Mass Unit

15. Atomic MassAtomic Mass
Atomic mass on the periodic table –Atomic mass on the periodic table –
averageaverage of all its isotopesof all its isotopes
Isotope – an Element with differingIsotope – an Element with differing
number of neutronsnumber of neutrons

16. Mass NumberMass Number
Mass number = total number of protonsMass number = total number of protons
and neutronsand neutrons
Identify isotopes by the mass numberIdentify isotopes by the mass number

17. Isotopic NotationIsotopic Notation
Hydrogen – 2Hydrogen – 2

has one proton and one neutronhas one proton and one neutron
Hydrogen – 3Hydrogen – 3

has one proton and two neutronshas one proton and two neutrons

18. Writing Isotopic SymbolsWriting Isotopic Symbols
X = element symbolX = element symbol
A = Mass NumberA = Mass Number
Z = Atomic NumberZ = Atomic Number
Total number of neutrons:Total number of neutrons:

Mass Number – Atomic number = number ofMass Number – Atomic number = number of
neutronsneutrons

19. Ions
Atoms that gain or lose electrons
Lose electrons – positive in charge
Gain electrons – negative in charge

20. Hydrogen that has lost an electron
H+1
Phosphorous that has gained 3 electron
P-3