the atom

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The Atom

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The Atom. Basic Atomic Theory. Atom = “indivisible” in Greek Atoms are indivisible and indestructible Atoms of same element are identical Compounds are formed by a combination of two or more different kinds of atoms Chemical reactions cannot change one element into another - PowerPoint PPT Presentation

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Page 1: The Atom

The Atom

Page 2: The Atom

Basic Atomic Theory Atom = “indivisible” in Greek Atoms are indivisible and

indestructible Atoms of same element are

identical Compounds are formed by a

combination of two or more different kinds of atoms

Chemical reactions cannot change one element into another Atoms only rearrange

Page 3: The Atom

Atoms are Indivisible and Indestructible? Not true!

Why? Nuclear reactions Subatomic particles

Page 4: The Atom

Electrons Discovered by J.J. Thompson

using a cathode ray tube Negatively charged (-1) Electron’s mass is 1/1840 Free moving around the

nucleus

Page 5: The Atom

Protons Discovered by Moseley Positively charged (+1) Proton’s mass is 1 (About 2000 times more

than an electron) Atomic # = # protons

No 2 elements have the same # of protons

Found in the nucleus of an atom

Page 6: The Atom

Neutrons Discovered by Chadwick No charge Same mass as proton (1) Found in the nucleus of an atom

Page 7: The Atom

Atomic Number Whole number Atomic # = # of proton Atomic # = # of electrons

(neutral) Atomic # = Z

Shorthand nuclear symbol Unique for every element

Page 8: The Atom

Atomic Number

Page 9: The Atom

Mass Number Whole number Mass # = # of protons + # of

neutrons Mass # = A

Shorthand nuclear symbol Isotopes of the same element

have different mass # Isotopes are the different kinds of

atoms within one element (C-12 and C-13)

Page 10: The Atom

Mass Number

Page 11: The Atom

Using Mass Number Mass # = # of protons + # of

neutrons To find # of protons

# protons = # electrons (neutral atom)

Need to know mass # and # of neutrons

To find # of neutrons: Need to know mass # and # of

protons

Page 12: The Atom

Nuclear Shorthand

Top number is A (mass #) Element symbol in the

middle Bottom number is Z (atomic

#)

Z

AElement Symbol

Page 13: The Atom

Atomic Mass

Listed on periodic table Does not equal mass # Given in atomic mass units

(amu) 1 amu = 1/12 the mass of C-12

atom Is not a whole number

Due to relative abundance of naturally occurring isotopes Weighted average

Page 14: The Atom

Finding Atomic Mass To calculate the atomic mass of

an element Multiply the mass of each isotope

by its percent abundance (expressed as a decimal) The quantity of a specific isotope that

occurs in a natural sample of an element Add the masses together

Also called average atomic mass

Page 15: The Atom

Very Funny… but what is wrong with this?

Page 16: The Atom

Isotopes Atoms of the same element

Have the same # of protons and electrons

Have a different number of neutrons Have a different mass number

Have the same physical and chemical properties and undergo the same chemical reactions

Have differing nuclear qualities Some isotopes of an element may be

radioactive Average atomic mass takes all of

the isotopes into consideration

Page 17: The Atom

Isotopes

Page 18: The Atom

Ions Atoms are neutral

Equal number of protons and electrons

Atoms can become charged by gaining or losing an electron Called ions

Ions are indicated with a (+) or (-) sign Cations are positive Anions are negative

Page 19: The Atom

Cations and Anions