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Take out reading check andDo Now:. 0.0000001 cm. 1. If 100,000,000 copper atoms were placed side by side, they would form a line 1 cm long. A)What is the number of atoms written in scientific notation. B)What is the diameter of 1 copper atom?. So how small is the atom?. Very small!

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take out reading check anddo now

Take out reading check andDo Now:

0.0000001 cm

1. If 100,000,000 copper atoms were placed side by side, they would form a line 1 cm long. A)What is the number of atoms written in scientific notation.

B)What is the diameter of 1 copper atom?

so how small is the atom
So how small is the atom?
  • Very small!
  • Smallest particle of an element that keeps the element’s properties
about 400 b c democritus
About 400 B.C. Democritus
  • a Greek philosopher
  • Proposed matter was composed of tiny, indivisible particles called “atomos”
  • origin of the word atom
late 1700 s
Late 1700’s

Proposed Law of Conservation of Matter - matter cannot be created nor destroyed

Antoine Lavoisier

Joseph Proust

Proposed Law of Definite Composition - a given compound always contains the same elements in the same proportions by mass

john dalton s atomic theory
John Dalton’s Atomic Theory

The atoms of any one element differ from those of any other element.

  • Each element is composed of tiny indivisible particles called atoms.
  • Atoms of different element combine in simple whole-number ratios to form compounds.
  • In chemical reactions, atoms are neither created nor destroyed. Atoms are rearranaged.
late 1800 s j j thomson
Late 1800’s J.J. Thomson
  • Experimented with cathode ray tubes (CRTs)







j j thomson
J. J. Thomson
  • Concluded cathode ray composed of negative particles - electrons
  • Unable to measure mass of electron, but found ratio of electron’s electrical charge to its mass - 1.76 x 108 Coulombs/gram

+ - +

- + - +

+ - +

- + -

  • Proposed Plum Pudding Model
do now
  • What were Dalton’s and Thompson’s contributions to atomic theory?
robert millikan
Robert Millikan
  • Performed Oil Drop Experimentin 1909
  • Found charge of electron to be 1.6 x 10-19Coulombs
  • Calculated mass of electron to be

~ 9.1 x 10-28 g

  • In 1896, Henri Becquerel accidentally discovered radioactivity while studying uranium salts
  • Spontaneous emission of energy from unstable nuclei
  • One type of radiation is alpha radiation. It is positively charged.
ernest rutherford in 1909
Ernest Rutherford in 1909
  • Performed Alpha Particle Scattering Gold Foil Experiment

1. Atoms mostly empty space

  • Findings ???

2. Atom contains a nucleus

3. Nucleus positively charged

what else is in the atom

Discovered by Rutherford in 1918 by

What else is in the atom?

Discovered by Chadwick in 1932

Proton –

Neutron -

do now1
  • What is an atom?
  • What subatomic particles does it contain?
  • Distinguish between the subatomic particles.
  • What is an isotope?
  • What is an ion?

Similar to the neutron

Very small compared to proton







In nucleus

Outside nucleus, in energy levels (clouds)

In nucleus

99.9% of mass

  • Are a different form of the atom that have the same number of protons in nucleus but a different number of neutrons.
  • Their masses vary
  • Chemically behaves

the same, may

affect radioactivity

  • Are atoms that have lost or gained electrons to become stable
  • Atoms that lose electrons are positively charged ( # protons > # electrons)
  • Atoms that gain electrons are negatively charge ( # protons < # electrons)
Using the Periodic Table and the information below, determine how many subatomic particles (protons, electron, and neutrons) are in…
  • 25Mg2+
  • Calcium – 40
  • 76Ge

Try your best!!!

Element name


25Mg 2+

Mass number

(must be provided)


= p - e

= p + n


Atomic number

(on periodic table)

= p (also e if not charged)


Calcium - 40

Mass number

do now2

Do Now…

Becky earned the following quiz grades… 87, 56, 94, 88 and 80. What is her quiz average?

Becky’s HW average was a 55 and her test average was a 75. Her teacher based her overall class grade on the following percentages: HW is 20%, Quiz is 50%, and Test is 30%. What is her overall grade in this class?

standard carbon 12
Standard: Carbon-12
  • This isotope of carbon was assigned a mass of exactly 12 amu
  • 1 amu (atomic mass unit) = 1/12 the mass of a carbon-12 atom
  • Carbon-12 has 6 protons and 6 neutrons
  • The mass of the proton is about 1 amu
  • The mass of the neutron is about 1 amu
since each isotope of given element has different masses the atomic mass is an average
Since each isotope of given element has different masses, the atomic mass is an average
  • Chlorine has two naturally occuring isotopes. Chlorine-35 has a mass of 34.969 amu and chlorine-37 has a mass of 36.966 amu.
  • Chlorine-35 has a natural abundance of 75.77% and chlrorine-37 has a natural abundance of 24.23.
  • What is atomic mass of chlorine?