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Chapter 2: Matter is Made of Atoms. Section 2.1 Atoms and Their Structures. Objectives. Relate historical experiments to the development of the atom, Illustrate the modern model of an atom, Interpret the information available in an element block of the periodic table.

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chapter 2 matter is made of atoms

Chapter 2: Matter is Made of Atoms

Section 2.1 Atoms and Their Structures


Relate historical experiments to the development of the atom, Illustrate the modern model of an atom, Interpret the information available in an element block of the periodic table

hypotheses theories and laws
Hypotheses, Theories and Laws

Solving a problem:

1) Observation - use senses to observe the behavior of matter

2)HYPOTHESIS– testable prediction

Hypotheses that are verified by repeating experiments

hypotheses theories and laws1
Hypotheses, Theories and Laws

EXPERIMENT: Investigation (with a control) designed to test a hypothesis

Hypotheses lead to scientific theories

THEORY: Explanation based on many observations and supported by the results of many experiments.

Ex: Dalton’s Atomic Theory

hypotheses theories and laws2
Hypotheses, Theories and Laws

SCIENTIFIC LAW: Fact of nature that is observed so often that it becomes accepted as truth.

A law can be used to make predictions, but does not explain why something happens

Example: Sun rises in the east

Theories can explain laws

early ideas about matter
Early Ideas about Matter

Greek Philosophers (2500 years ago)

4 Fundamental Elements- air, earth, fire, and water

Questioned if matter could be divided endlessly into smaller pieces or if there was an ultimate small particle of matter

Aluminum Foil

democritus dem ock rit is 460 370 b c
Democritus (dem-ock-rit-is) 460-370 B.C.

Proposed the world is made up of empty space and the smallest particles of matter are called ATOMS

  This introduced the atomic theory of matter

Different types of atoms exist for every type of matter

modern atomic theory
Modern Atomic Theory

Antoine Lavoisier (Luh-voh-zee-ay) 1782

Concluded that when a reaction occurs, matter is neither created nor destroyed

Law of Conservation of Matter

conservation of matter and recycling
Conservation of matter and recycling

Atoms are neither created nor destroyed

You can’t throw anything away because there is no “away”

Recycling Nitrogen- Nitrogen is atmosphere is converted into compounds used on Earth, then returned to atmosphere (p. 53, Figure 2.4)

Recycling plastic, aluminum and glass- reusing atoms in these materials, we imitate nature and conserve natural resources (in natural processes atoms are recycled)

joseph proust 1799
Joseph Proust 1799

Observed that the elements that composed compounds were always in a certain proportion by mass- LAW OF DEFINITE PROPORTIONS

Ex: water is always 11% H and 89% O by mass

dalton s atomic theory of matter 1803
Dalton’s Atomic Theory of Matter (1803)

Theory essentially intact with small modifications to accommodate new discoveries

Main Points of Dalton’s Atomic Theory

1. All matter is made up of atoms

2. Atoms are indestructible and cannot be divided into smaller particles.

3. All atoms of one element are exactly alike, but atoms are different for different elements

Late 19th century, experiments began to suggest that atoms are made up of even smaller particles (electrons, protons, neutrons)

atomic structure
Atomic Structure

Today we know that atoms are made of smaller particles and Atoms of the same element can be nearly the same (but not exactly)

 Cathode Ray Tube Experiment- J.J. Thomson (1897)

Vacuum tube- positive and negative electrode- ray travels through tube from the – to the +, rays bent toward + and away from the –

Electrons, Protons, Neutrons

ELECTRON- negatively charged subatomic particle

Mass equal to 1/1837 the mass of a Hydrogen atom

PROTON- positively charged subatomic particle

The amount of charge on an electron and a proton is equal and opposite

The mass of a proton is much greater than the mass of an electron (slightly less then a Hydrogen atom)

atomic structure1
Atomic Structure

Until 1910, it seemed that atoms were made up of equal numbers of electrons and protons

J.J. Thomson discovered that Neon consisted of atoms of two different masses

atomic structure2
Atomic Structure

Ernest Rutherford- 1909 “Gold Foil Experiment” (p.62, Fig 2.9)

+ charged particles (alpha particles) sent through a gold foil – most went straight through (empty space), few deflected (hit nucleus)

Revealed the arrangement of the atom- 1911

Atom is nearly all empty space with a small, dense, positively charged core called a NUCLEUS

atomic structure3
Atomic Structure

Atoms of an element that are chemically alike but different in mass are called ISOTOPES

The discovery of isotopes – atoms must contain a third type of particle that explains mass differences

NEUTRON- neutral subatomic particle

Mass is equal to that of a proton but has no electrical charge

Existence of the neutron was confirmed in early 1930s

even smaller particles
Even smaller particles…

Quarks – small particles of matter that make up protons and neutrons.

6 “flavors” or types – top, bottom, charm, strange, up and down

An arrangement of 3 of these will form a proton, another arrangement will form a neutron.


Subatomic particles produced by the decay of radioactive elements

Elementary particles that lack an electric charge

F. Reines would say, "...the most tiny quantity of reality ever imagined by a human being


Copiously produced in high-energy collisions

Traveling essentially at the speed of light

Unaffected by magnetic fields neutrinos Their unique advantage arises from a fundamental property: they are affected only by the weakest of nature's forces (but for gravity) and are therefore essentially unabsorbed as they travel cosmological distances

atomic number and masses
Atomic number and masses

ATOMIC NUMBER: Number of protons in the nucleus of an atom of that element

# of protons determines the identity of an element and many of its chemical and physical properties

Atomic number also tells us the number of electrons in a neutral atom of an element (p+ = e-)

atomic number and masses1
Atomic Number and Masses

MASS NUMBER: Sum of the protons and neutrons in the nucleus of an atom

Mass # = p+ + n0

n0 = Mass # - p+

Example: # of neutrons: mass # = 19 (Flourine)

n0 = 19 - 9 = 10

atomic number and masses2
Atomic Number and Masses

Isotopes have different mass numbers because they have different numbers of neutrons (they have the same atomic number) 

Isotopes are identified by placing the mass number after the name or symbol of the element

Ex: Li-7, Li-6

Ne-20, Ne-21, Ne-22

periodic table information
Periodic Table information

Each box contains: element, state, atomic number, symbol and average atomic mass (weighted average of the naturally occurring isotopes)

Atomic mass example:

Chlorine has 2 isotopes- Cl-37 and Cl-35

24.2% is Cl-37 and 75.8% is Cl-35

So the atomic mass is 35.45


Protons, Neutrons, Electrons

Particle Symbol Charge Mass in grams Mass in u

Proton p+ 1+ 1.67 x 10-24 1.01

Neutron no 0 1.67 x 10-24 1.01

Electron e- 1- 9.11 x 10-28 0.00055

u – ATOMIC MASS UNIT (devised mass unit)

1 u = 1/12 the mass of a carbon-12 atom

1 u  mass of single proton or neutron