Download atoms

Chapter Menu
Section 2.1
Atoms and Their Structures
Section 2.2
Electrons in Atoms
Click a hyperlink to view the corresponding slides.
Atoms and Their Structures
• Relate historic experiments to the
development of the modern model of the atom.
• Illustrate the modern model of an atom.
• Interpret the information available in an
element block of the periodic table.
Atoms and Their Structures
energy: the capacity to do work
Atoms and Their Structures
atom
theory
neutron
atomic theory
scientific method
nucleus
law of definite
proportions
scientific law
atomic number
electron
mass number
hypothesis
proton
isotope
experiment
isotope
atomic mass unit
An atom is made of a nucleus containing
protons and neutrons; electrons move
around the nucleus.
Early Ideas About Matter
• Greek philosophers thought that matter was
composed of four elements: earth, water, air,
and fire.
Early Ideas About Matter (cont.)
• Democritus (460–370 B.C.) first proposed
that the world is made up of empty space
and atoms, the smallest particle of a given
type of matter.
• The idea that matter is made up of
fundamental particles called atoms is known
as the atomic theory of matter.
Modern Atomic Theory
• Antoine Lavoisier concluded that when a
chemical reaction occurs, matter is neither
created nor destroyed but only changed.
This conclusion became known as the law
of conservation of matter.
Modern Atomic Theory (cont.)
• In 1799, Joseph Proust proposed the law of
definite proportions, or the principle that the
elements that comprise a compound are
always in a certain proportion by mass.
Composition
of iron sulfide
Modern Atomic Theory (cont.)
• Dalton’s Atomic Theory
– All matter is made of atoms.
– Atoms are indestructible and indivisible.
– All atoms of one element are exactly alike,
but they are different from atoms of other
elements.
Modern Atomic Theory (cont.)
• In natural processes,
atoms are not
destroyed; they are
recycled.
Hypotheses, Theories, and Laws
• A hypothesis is a prediction that can be
tested to explain observations.
• An experiment is an investigation with a
control designed to test a hypothesis.
• A theory is an explanation based on many
observations and supported by the results of
many investigations.
Hypotheses, Theories, and Laws (cont.)
• The systematic approach scientists use to
answer questions and solve problems is
called the scientific method.
Hypotheses, Theories, and Laws (cont.)
• A scientific law is a fact of nature that is
observed so often that it becomes
accepted as truth.
– The Sun rising in the east each morning is
a scientific law.
The Discovery of Atomic Structure
• From Thomson’s experiments, scientists
concluded that atoms were composed of
electrically-charged particles.
• An electron is a negatively-charged particle.
• A proton is a positive-charged subatomic
particle.
• A neutron is a subatomic particle that has a
mass equal to a proton by no electrical
charge.
The Discovery of Atomic Structure (cont.)
• Atoms of an element that are chemically
alike but differ in mass are called isotopes.
The Discovery of Atomic Structure (cont.)
• Scientists proposed different atomic
models.
The Discovery of Atomic Structure (cont.)
• Rutherford’s gold foil experiment revealed
an atomic arrangement far different from
earlier models.
The Discovery of Atomic Structure (cont.)
• Rutherford’s team proposed a new model of
the atom that included a nucleus, a small
dense, positively-charged central core.
Rutherford’s Model
Modern Model
Atomic Numbers
• The atomic number refers to the number
of protons in the nucleus of an atom.
• The mass number is sum of the protons and
neutrons in the nucleus of an atom.
• Isotopes of an element have different mass
numbers because they have different
numbers of neutrons.
Atomic Numbers (cont.)
Atomic Mass
• To easily compare the masses of individual
atoms, scientists devised a different unit of
mass, the atomic mass unit (u), which is
approximately the mass of a single proton
or neutron.
Atomic Mass (cont.)
Atomic Mass (cont.)
• Each box of the periodic table contains
several pieces of information about an
element.
Atomic Mass (cont.)
• To calculate the weighted average atomic
mass, you first need to calculate the mass
contribution of each isotope.
Naturally Occurring Isotopes of Chlorine
Section Assessment
The idea that matter is made up of
fundamental particles called atoms is
known as ___.
A. the law of conservation of matter
B. the law of conservation of mass
C. the atomic theory of mass
D. the atomic theory of matter
Section Assessment
Isotopes of an element have different
mass numbers because they have
different numbers of ___.
A. protons
B. electrons
C. neutrons
D. nuclei
Electrons in Atoms
• Relate the electron to modern atomic theory.
• Compare electron energy levels in an atom.
• Illustrate valence electrons by Lewis electron
dot structures.
Electrons in Atoms
atom: smallest particle of a given type of matter
Electrons in Atoms
electromagnetic
spectrum
electron cloud
emission spectrum
Lewis dot diagram
valence electron
energy level
Each element has a unique
arrangement of electrons.
Electrons in Motion
• Niels Bohr (1885–1962) proposed that
electrons must have enough energy to
keep them in constant motion around the
nucleus.
• Electrons occupy orbits
of only certain amounts
of energy.
The Electromagnetic Spectrum
• High-voltage electricity or electromagnetic
radiation, or radiant energy, can increase
the energy of an electron.
• Electromagnetic radiation travels in the form
of waves that have
both electric and
magnetic properties.
The Electromagnetic Spectrum (cont.)
• The electromagnetic spectrum is the
whole range of electromagnetic radiation.
– radio waves
– radiant energy
– visible light
• Higher-frequency electromagnetic waves have
higher energy than lower-frequency waves.
The Electromagnetic Spectrum (cont.)
Electrons and Light
• Each element emits a different emission
spectrum, or a spectrum of light released
from excited atoms of the element.
Electrons and Light (cont.)
• Because electrons can have only certain
amounts of energy, they can move around
the nucleus only at distances that
correspond to those amounts of energy.
Electrons and Light (cont.)
• The regions of space in which electrons
can move about the nucleus of an atom are
called energy levels.
The Electron Cloud Model
• The electron cloud is the space around
the nucleus of an atom where the atom’s
electrons are most likely to be found.
The Electron Cloud Model (cont.)
• Each energy level can hold a limited
number of electrons.
– First energy level—2 electrons
– Second energy level—8 electrons
– Third energy level—18 electrons
The Electron Cloud Model (cont.)
• The electrons in the outermost energy level
are called valence electrons.
The Electron Cloud Model (cont.)
• Many of the chemical and physical
properties of an element are directly
related to the number and arrangement of
valence electrons.
The Electron Cloud Model (cont.)
• A Lewis dot diagram is a diagram where
dots are placed around the chemical
symbol of an element to illustrate the
valence electrons.
Section Assessment
The first energy level of an atom holds a
maximum of ___ electrons.
A. one
B. two
C. four
D. eight
Section Assessment
In a Lewis dot diagram, each dot
represents a(n) ___.
A. neutron
B. proton
C. electron
D. valence electron
Chemistry Online
Study Guide
Chapter Assessment
Standardized Test Practice
Image Bank
Concepts in Motion
Key Concepts
• Scientists make hypotheses based on observation.
• Dalton’s atomic theory states that matter is made up of
indestructible atoms.
• Experiments in the late nineteenth and early twentieth
centuries revealed that the mass of an atom is
concentrated in a tiny nucleus.
• The number of protons in an atom’s nucleus is called the
atomic number and equals the number of electrons in
the atom.
• Atoms of the same element always have the
same number of protons and electrons.
Key Concepts
• Electrons move around an atom’s nucleus in specific
energy levels.
• Energy levels are spherical regions in which electrons
are likely to be found.
• The greater the energy of the level, the farther from the
nucleus the level is located.
• Electrons can absorb energy and move to a higher
energy level.
• Lewis dot diagrams can be used to represent the
valence electrons in a given atom.
Early Greek philosophers proposed that
matter was a combination of what four
fundamental elements?
A. air, fire, wind, earth
B. fire, air, earth, water
C. hot, dry, cold, wet
D. water, wind, fire, ice
What is an explanation based on many
observations and supported by the
results of many investigations?
A. theory
B. experiment
C. hypothesis
D. scientific law
What is the systemic approach scientists
use to answer questions and solve
problems?
A. experiment
B. hypothesis
C. scientific law
D. scientific method
What is the distance between
corresponding points on two consecutive
waves?
A. spectrum
B. rate
C. wavelength
D. frequency
Atoms in group 2 of the periodic table
have how many valence electrons?
A. 1
B. 2
C. 13
D. 18
The mass of a proton is ___ the mass of
an electron.
A. greater than
B. less than
C. equal to
The mass of a neutron is ___ the mass of
a proton.
A. greater than
B. less than
C. equal to
The atomic number determines the
identity of an element, as well as many of
its chemical and physical properties.
A. true
B. false
What kind of properties do
electromagnetic radiation waves have?
A. electric
B. magnetic
C. nuclear
D. A and B
The energy of higher-frequency
electromagnetic waves is ____
lower-frequency waves.
A. higher than
B. lower than
C. the same as
Click on an image to enlarge.
Click on an image to enlarge.
Rutherford’s Model
Modern Model
Naturally Occurring Isotopes of Chlorine
Table 2.1
Particles of an Atom
Figure 2.4
The Nitrogen Cycle
Figure 2.9
Rutherford’s Experiment
Figure 2.20
The Emission Spectrum
Figure 2.21
Energy Levels in an Atom
To use this Interactive Chalkboard product:
Click the Forward button to go to the next slide.
Click the Previous button to return to the previous slide.
Click the Home button to return to the Chapter Menu.
Click the Return button in a feature to return to the main presentation.
Click the Exit button or press the Escape key [Esc] to end the slide show.
Click the Help button to access this screen.
Click the Chapter Resources button to view available resources for the chapter.
These resources include Chemistry Online, Study Guide, Chapter Assessment,
Standardized Test Practice, Image Bank, and Concepts in Motion.
Concepts in Motion pieces can also be accessed on relevant lecture note slides.
This slide is intentionally blank.