Atoms, Ions, & IsotopesOh, My!Part II

The atoms of different elements contain different numbers of protons. The number of protons in the nucleus of an atom is called the atomic number.

The smallest atom is hydrogen with only one proton in its nucleus. The largest naturally occurring atom is uranium with 92 protons in its nucleus. You can tell what element an atom is by the number of protons. If you change the number of protons, then you change the identity of the element.

The atomic number is the number of protons and identifies what element an atom is.

However, the number of neutrons can vary in the same type of element. When atoms of the same element have a different number of neutrons they are called isotopes. Carbon-12

Carbon-13

Carbon-14

The number of protons and the number of neutrons added together make up the mass of the atom. That is called its mass number.

mass # = protons + neutronsOR

m# = p + nCarbon-12

Carbon-13

Carbon-14

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Atom CharacteristicsAtom Characteristics

• The atomic mass is the mass of the protons plus the mass of the neutrons.

Atomic mass is recorded in the SI units: atomic mass units (amu).

Protons and neutrons each are given an amu of 1.

Electrons have a mass of nearly zero.

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Decoding Atom InformationDecoding Atom Informationfrom the Periodic Table from the Periodic Table

CCarbo

n

6

12.0

Atom’sSymbol

Atom’s Name

Atomic Number

Atomic Mass

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Decoding Atom InformationDecoding Atom Informationfrom the Periodic Table from the Periodic Table

Carbon

12.012.0

Atomic number# of protons = # of electrons

Atomic mass = # of protons plus the # of neutrons

66

C

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How can I ever figure out the number of protons, electrons, and neutrons in a neutral atom?! HELP!!!!!

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APE MAN to the rescue!

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A = P = E M - A = Nt omi c

Numbe r

R o t ons

l ec t r ons

(if neutral)

ass

t omi c

Numbe r

eu t r ons

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Using APE MANLet’s say you’re trying to find the number of protons,

electrons, and neutrons of a neutral atom of Sodium (Na).

Fill out the information you have:Atomic number is 11. Mass is 23.

WAIT A MINUTE!!! WHERE DID YOU GET THE MASS OF 23?!

To find the mass of the most common isotope of an atom, look at the atomic mass on the periodic table and

round it to the nearest ones place.

Sodium has a mass of 22.990. Round it to the ones place and you get 23.

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Using APE MAN (continued)Sodium:Atomic number is 11. Mass is 23.

A=P=E M-A=N

11=P=E 23-11=N

11=11=11 23-11=N

11=11=11 23-11=12So...

Sodium has 11 protons, 11 electrons, and 12 neutrons in a neutral atom of its most

common isotope.

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Let’s Try One Together…How many protons, electrons, and

neutrons are in an atom of the most common isotope of fluorine?

A=P=E M-A=N

9=P=E 19-9=N9=9=9 19-9=10

Protons: 9, Electrons: 9, Neutrons: 10

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Now You Try One…How many protons, electrons, and

neutrons are in an atom of the most common isotope of Neon?

A=P=E M-A=N

10=P=E 20-10=N

Protons: 10, Electrons: 10, Neutrons: 10

10=10=10 20-10=10

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