Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 How Atoms Differ.

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 3

How Atoms Differ


Section 3 The Atom

Objectives

• Describe the size of an atom.

• Name the parts of an atom.

• State how atoms of different elements differ.

• State how isotopes differ.

• Calculate atomic masses.

• Describe the role of electrons in an atom.

Chapter 4


Section 3 The Atom

How Small Is an Atom?

• Scientists know that aluminum is made of average-sized atoms. An aluminum atom has a diameter of about 0.00000003 cm.

Chapter 4


Section 3 The Atom

What Is an Atom Made Of?

• The Nucleus •Protons are positively charged particles •Neutrons have no electrical charge.

• Outside the Nucleus •Electrons are the negatively charged particles in electron clouds.

Chapter 4


Section 3 The AtomChapter 4

Parts of an Atom


Section 3 The Atom

What Is an Atom Made Of?

• The Nucleus •positively charged particles called protons.•Each proton has a mass of about 1 amu.

• The SI unit used to express the masses of particles in atoms is the atomic mass unit (amu).

• Neutrons•In nucleus that have no electrical charge.•Neutrons have a mass of about 1 amu

Chapter 4


Section 3 The Atom

What Is an Atom Made Of?, continued

• Outside the Nucleus •Electrons are negatively charged particles in atoms. •Electrons are found around the nucleus within electron clouds.

• The charges of protons and electrons are opposite but equal, so their charges cancel out.

• Because an atom has no overall charge, it is neutral.

Chapter 4


Section 2 The Atom

How Do Atoms of Different Elements Differ?

• Starting Simply •The hydrogen atom has one proton and one electron.

•The helium atom has two protons, two neutrons, and two electrons.

Chapter 4


Section 2 The Atom

How Do Atoms of Different Elements Differ?, continued

• Building Bigger Atoms For bigger atoms, simply add protons, neutrons, and electrons.

• Protons and Atomic Number •atomic number = number of protons•Atomic mass = number of protons + number of neutrons

Chapter 4


Atoms

• Atoms are electrically neutral, so:

• Protons = Electrons = Atomic Number

• Neutrons does not have a specific relationship to protons

• Atomic Mass = Protons + Neutrons– Electrons have almost no mass


Reading the Periodic Table

Name

Atomic Number

Symbol

Avg. Atomic Mass


Periodic Table


Reading the Periodic Table - Quiz• How Many Protons are in

– Boron (B)– Platinum (Pt)

• How many electrons are in:– Radium (Ra)– Magnesium (Mg)

• An element contains 66 electrons. What is it?• An element contains 14 protons. What is it?

578

8812

Dysprosium

Silicon


Calculating Protons & NeutronsElement Atomic

MassAtomic Number

Protons Neutrons Electrons

B

24.305

8

19

11 5 5 56

Mg 12 1212 12

O 16 8 8 8

K 19 20 1939


Why are Atomic Masses not Even Numbers?

• What is the atomic mass of Carbon (C)?– 12.011

• What is the atomic mass of Chlorine (Cl)?– 35.453

• If Protons = 1 and Neutrons = 1, where does the .453 come from?


Why not whole Numbers?

• Mass of both Neutron and Proton is 1.67x10-24

• Small units/hard to work with

• Scientists set standard based on Carbon 12– 1 atomic mass unit = 1/12 of carbon atom

• So Silicon is 29.974 instead of 30

– This is only part of the reason…


Section 2 The Atom

Isotopes• have the same number of protons but different

numbers of neutrons.

Chapter 4


Isotopes

• Another thing Dalton got wrong

• Isotopes occur as a mixture in nature– Example Potassium:

• 93.25% have 20 neutrons• 6.7302% have 22 neutrons• 0.117% have 21 neutrons• ALL have 19 Protons and 19 Electrons

• Isotopes have the Same Atomic Number but a Different Atomic Mass


Section 2 The Atom

Isotopes, continued

• Telling Isotopes Apart •by its mass number.

• How Many Neutrons?•Calculate Neutrons = Atomic Mass – Atomic number

• Properties of Isotopes •An unstable atom has a nucleus that will change over time. •This type is radioactive.

Chapter 4


Section 2 The Atom

Isotopes, continued

Chapter 4


Section 2 The Atom

Isotopes, continued

• Naming Isotopes•Write the name of the element followed by a hyphen and the mass number.

•Example: C-14 is Carbon 14 (8 neutrons) instead of 6 (C-12 is normal)

• Calculating the Mass of an Element •The atomic mass of an element is the weighted average of the masses of the isotopes of that element.

Chapter 4


Section 3 The Atom

Math FocusChapter 4

Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 How Atoms Differ.

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