Mendeleev’s RoleMendeleev’s RoleChapter 4.2Chapter 4.2

Organization and Organization and discovery discovery

Periodic table historyPeriodic table history

John Newlands 1800’sLaw of octaves

. 63 elements

Law of octaves – elements group in 8’s because they repeated theSame number of valence electrons

►Dmitri MendeleevDmitri Mendeleev►2nd person to work on 2nd person to work on the Periodic tablethe Periodic table

►Notice that elements Notice that elements didn’t didn’t

Go together – Go together – some some react violently react violently

► Arranged by atomic Arranged by atomic MassMass

►Henry Mosley Henry Mosley ►group them by atomic group them by atomic number and they would number and they would have a better have a better pattern/flowpattern/flow

►Physical and chemical Physical and chemical properties are functions properties are functions of the atomic #of the atomic #

►Periodic law- elements Periodic law- elements with similar properties with similar properties occur in a regular patternoccur in a regular pattern

- Elements are arranged by Elements are arranged by increasing atomic numberincreasing atomic number

- Certain properties reoccurCertain properties reoccur- Predictions can be madePredictions can be made

Organization of the PTOrganization of the PT

►Columns go up and Columns go up and downdownThey are called families They are called families or groupsor groups

There are 18 diff familiesThere are 18 diff families

Organization of the PTOrganization of the PT►Rows go from left to rightRows go from left to right

They are called periods They are called periods Different propertiesDifferent propertiesValence electron increase.Valence electron increase.Oxidation number changesOxidation number changes

Oxidation NumberOxidation Number►The oxidation number is The oxidation number is the number of electrons the number of electrons that an element wants that an element wants to gain or give up to to gain or give up to become happy(Stable). become happy(Stable). Shells need 8 to be Shells need 8 to be

►except 1except 1stst shell (need 2) shell (need 2)

Oxidation NumberOxidation Number

►Families valence e- go Families valence e- go from 1 to 8 from 1 to 8

►Oxidation numbers go Oxidation numbers go from +1,+2,+3,+/-4, -3,-from +1,+2,+3,+/-4, -3,-2,-12,-1

►Atomic numberAtomic number Symbol Symbol►Protons &Protons &►electronselectrons

►Element name Element name

► Atomic Mass Atomic Mass

((Protons +Protons + Neutrons)Neutrons)

Amu= SI unit for atomic massAmu= SI unit for atomic mass

IonsIons

►Ions gain/lose electrons Ions gain/lose electrons to become happy and to become happy and by using the oxidation by using the oxidation number you can number you can determine how many.determine how many.

Isotopes are atoms that gain/lose neutrons and their mass changes.

The mass on the periodic table is the average of all isotopes

Changing An Atom