Atomic Structure & Isotpes

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Structure of the Atom

• nucleus nucleus – positive protons and neutral neutrons positive protons and neutral neutrons – 99.9% of the atom’s mass is here– up to 100,000 times smaller than the entire atom

• negative electrons are in space “around” the nucleus.electrons are in space “around” the nucleus.

NucleusNucleus

Electron cloudElectron cloud

Bill Nye atom size (start at 3:55)

sub-atomic particlessub-atomic particles• Protons (pProtons (p++))

– + electrical charge+ electrical charge– same as atomic # on periodic tablesame as atomic # on periodic table– 1.007 atomic mass units (amu) 1.007 atomic mass units (amu) but we can but we can round to 1 round to 1

amu amu (mass = 1.672623 x 10(mass = 1.672623 x 10-24-24 g) g)

• Electrons (eElectrons (e--))– negative electrical chargenegative electrical charge– same as + protons in a neutral atomsame as + protons in a neutral atom– 0.0005 amu 0.0005 amu but we can round to 0but we can round to 0

• Neutrons (nNeutrons (noo))– no electrical chargeno electrical charge– mass = 1.009 amu mass = 1.009 amu but we can round to 1 amubut we can round to 1 amu

Particle Charge Mass

(atomic mass units)

Location

Proton positive

+

1 nucleus

Neutron neutral

Ø

1 nucleus

Electron negative

-

0.0006

or Ø

orbit, level, cloud

Learning Check

An atom has 14 protons and 20 neutrons.

A. Its atomic number is1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. The number of electrons is1) 14 2) 6 3) 20

Even smaller particlesEven smaller particles

• quarks– make protons & neutronsmake protons & neutrons– 6 types6 types

He

Isotopes • same element but differ in their number of

neutrons• the mass number on periodic table is the

WEIGHTED AVERAGE MASS of all the isotopes of that element– this is based on an isotope’s natural abundance

• the percentage of each isotope of an element that occurs in nature

2.3

Chemical symbols for isotopes

• two different ways to write isotopes– example sodium

• sodium- 23– only shows total mass (23) of the sodium isotope

• 23 Na– shows the total mass (23) and the atomic # (11) of

the sodium isotope

11

XMass Number

Atomic NumberElement Symbol

Isotopes?

Which of the following represent isotopes of the same element? Which element?

234 X   234 

X235 

X238 

X

  92   93    92 92

How many protons, neutrons, and electrons are in-- C14

6

How many protons, neutrons, and electrons are in--

C116

6 protons, 8 (14 - 6) neutrons, 6 electrons

6 protons, 5 (11 - 6) neutrons, 6 electrons

Do You Understand Isotopes?

H11 H 2

1 H 31

U23592 U238

92