1

Negative particles

Positive particles

Neutral particles

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Why do most of the alpha particles pass through?

31 angstrom = 1 x 10-10 m

4

nucleus

Protoncharge = +, mass = 1.0073 amuatomic mass units: 1amu = 1.6605402 x 10-24 g

Neutroncharge = neutral, mass = 1.0087

Electroncharge = 1-, mass = 5.4586 x 10-4 amu

Almost all the mass is in the nucleus,and

almost all the volume is due to the electrons!

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Almost all the mass is in the nucleus,and

almost all the volume is due to the electrons!

One penny If this penny consisted of just nuclearmaterial it would weigh……...

190,000,000 TONS!!!

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In a neutral atom, the number of (+) protons = the number of (-) electrons

And.. The number of protons is equal to the atomic number of the element.

Since the mass of an atom is almost entirely located in the nucleus, the mass number is equal to:the number of protons PLUS the number of neutrons

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The lower numbers found on most periodictables are the ATOMIC MASSES (WEIGHTS)NOT the ATOMIC MASS NUMBER!

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Isotopes: same element, different atomic mass.

How can this be?

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Isotopes: same element, different atomic mass.

How can this be?

If it’s the same element ,the number of protons

can’t change. So what must change?

Isotopes: same element, different number of neutrons.

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11C 12C 13C 14C

ISOTOPES

No. protons:

No. Electrons:

No. neutrons:

6 6 6 6

6 6 6 6

5 6 7 8

11

N147

N157

99.63%14.0031 amu

0.37%15.0001 amu

ISOTOPES OF NITROGEN

12

C126

C136

C-12 basis for the atomic mass scale

C146

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Atomic mass or weight: the weighted average of the atomic masses of all naturally occurring isotopes present.

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35.45Cl

Atomic #

Atomic mass or weight

Cl3517 75.53%

Cl3717

24.47%

Naturally occurring ISOTOPES:

34.9689 amu

36.9659 amu

x 0.7553 = 26.412

x 0.2447 = 9.045

35.45Atomic mass onperiodic table

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“Losers”Metals lose e-’s in chemical reactions

Boy there area lot oflosers!

15non-metals: gain electrons (or share)

metalloids:

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Why is O a non metal and Po a metal?

Nucleus

17

1

234

56

7

periods

periods

18

1

234

56

7

Groups or families

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Molecular Compounds: (molecules)

CO2

CO

H2O2

O3

H2O

O2

CH4

C2H4

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7 diatomic elements

6 + 1 = 7

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Molecular structures:

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Molecular and Empirical Formulas:

Simplest Form

Actual formula

butene: C4H8 molecular or empirical?

What is the empirical formula? CH2

Carbon dioxide: CO2 empirical or molecular?

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Ions and ionic compounds:

cation: positive charge (lost e-’s)

Na+ 11 protons and only 10 electrons

anion: negative charge (extra e-’s)

Cl -17 protons and 18 electrons

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