II- II- HowHow AtomsAtoms DifferDiffer

A-A- All atoms of an elementelement have the same numbernumber of protonsprotons. The number of

protons determinesdetermines what the elementelement is.

1- 1- AtomicAtomic NumberNumber is the numbernumber of protonsprotons of an

atom.

2- 2- MassMass NumberNumber:: is the total numbernumber of ProtonsProtons and NeutronsNeutrons in an atomatom.

a-a- To find the numbernumber of neutronsneutrons in an atomatom all you do is

subtractsubtract the atomicatomic numbernumber from the massmass numbernumber.

Mass Number

B-B-IsotopesIsotopes:: Atoms of the samesame element with the samesame

atomic number but a differentdifferent number of neutronsneutrons.

III-III-ClassifyingClassifying ElementsElements::

A-A-TheThe PeriodicPeriodic TableTable:: Was created by MendeleevMendeleev, he put the elementselements with the same characteristicscharacteristics into columnscolumns.

1-1-The elements lineline up in increasingincreasing atomicatomic numbers.

B- B- ArrangementArrangement ofof TableTable::

1-1-Each rowrow is called a periodperiod and each columncolumn is called a groupgroup.

2-2-If you know somethingsomething about an elementelement in a

groupgroup you know somethingsomething about

them allall.

3-3-Each box has an element’s symbolsymbol, name, atomicatomic numbernumber, massmass number, and the number of electronselectrons in each energy energy levellevel.

13

26.98

AlAluminum

2

8

3

Atomic Number

Number of electrons in each energy level

Average atomic mass

Symbol

Name