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Chapter 11 Section 2
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8/14/2019 The Atom Ch11.2 8th PDF (Information obtained from: Holt Science and Technology: Physical Science. New York: Henry Holt & Co, 2007. Print.)
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A penny contains 2 x 10²² atoms of copperand zinc (20,000,000,000,000,000,000,000)
Atoms are very small!!
An aluminum atom has a diameter of 0.00000003cm
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Protons
Neutrons
Electrons
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Small, dense, positively charged center of theatom
Contain most of the atom’s mass
Protons & neutrons are found here
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Positively charged particles in the nucleus
Mass of a proton: 1.7 x 10ˉ² 4g or
.000000000000000000000017
New unit for particles of atoms: Atomic Mass Unit (AMU)
◦ SI unit used to express the masses of particles in atoms◦ Each proton has a mass of about 1 amu
8/14/2019 The Atom Ch11.2 8th PDF (Information obtained from: Holt Science and Technology: Physical Science. New York: Henry Holt & Co, 2007. Print.)
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Particles in the nucleus that have no electricalcharge
A little large than protons
So close in size that they are also considered1 amu
http://www.phscale.net/atom-model.gif
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Electrons : negatively charges particles inatoms
Found around the nucleus in electron clouds
Very small compared to neutrons & protons
It takes ~1,800 electrons = 1 proton
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What makes atoms different from each other?
Atoms do not have the same number of
protons, electrons, and neutrons
Build an atom to see:◦ 1 proton, 1 electron, 0 neutrons = Hydrogen◦
2 protons, 2 neutrons, 2 electrons = Helium
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The number of protons = atomic number
All atoms of an element have the sameatomic number
Hydrogen: atomic number 1, protons 1Carbon: atomic number 6, protons 6
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An atom that has the same number of protons ( or the same atomic number ) asother atoms of the same element do but thathas a different number of neutrons ( differentatomic mass )
Ex: Isotopes of Hydrogen◦
1 proton, 1 electron◦ 1 proton, 1 neutron, 1 electron
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http://www.radiation-scott.org/timeline/isotope_definition_LARGE.jpg
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Each element has a limited number of isotopes that are found in nature
Some are unstable (nucleus changes overtime) = radioactive
Isotopes of the same element share similar
properties◦ Ex: Oxygen isotopes: 8,9, or 10 neutrons – all are
colorless, odorless gases at room temp.
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Identified by its mass number (sum of protons & neutrons in an atom)
Why aren’t electrons included in mass #?
Ex: Boron isotope – Fig. 5 pg. 322
◦ Mass number = protons + neutrons
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Write the name of the element followed by ahyphen and the mass number
Ex: Hydrogen-1 : 1 proton, no neutronHydrogen-2 : 1 proton, 1 neutron
Ex: Carbon-12 : mass number 12, atomic
number 6, neutrons 6◦ Mass number - # of protons = # of neutrons
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What are the forces acting between theseparticles in an atom?
4 main forces: give atoms their structure &properties◦
◦
◦ : nucleus stays together because of it◦ : important in radioactive atoms
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What is an atom’s mass number equal to?
How is the atomic mass of an elementcalculated?
How do isotopes differ from one another?
