Properties of Atoms and the Periodic Table. STRUCTURE OF THE ATOM Section 1
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- Slide 1
- Properties of Atoms and the Periodic Table
- Slide 2
- STRUCTURE OF THE ATOM Section 1
- Slide 3
- An element of matter is made up of one type of atom Atoms are
composed of particles called protons, neutrons, and electrons
Protons-positive charge Electrons-negative charge Neutrons-no
charge Protons and neutrons are in centrally-located nucleus
surrounded by a cloud containing electrons Structure of the
Atom
- Slide 4
- Scientists hypothesize that electrons are not composed of
smaller particles Protons and neutrons are made up of smaller
particles called quarks The search for the exact composition of
protons and neutrons is ongoing Quarks
- Slide 5
- Many different models of the atom were proposed throughout the
years Aristotle argued that atoms didnt even exist John Daltons
provided evidence that atoms existed His model was a simple sphere
Joseph Thomson proposed the plum-pudding model Ernest Rutherfords
model included a nucleus Niels Bohr suggested that electrons travel
in fixed orbits around the nucleus Atomic Models Daltons Model
Rutherford Model Thomson Model Bohr Model
- Slide 6
- By 1926, scientists developed the electron cloud model of an
atom This is the currently accepted model The electron cloud is the
area around the nucleus where its electrons are most likely to be
found The cloud is 100,000 times larger than the diameter of the
nucleus The Electron Cloud Model
- Slide 7
- MASSES OF ATOMS Section 2
- Slide 8
- All elements are represented by a chemical symbol The symbols
consist of one capital letter or a capital letter and one or two
lowercase letters Some symbols are the first letter of the elements
name Oxygen O Some are derived from Latin Silver ArgentumAg Some
are name in honor of scientists Some are named for where they were
discovered The symbols are recognized worldwide Atomic Symbols
- Slide 9
- The number of protons in an atoms is known as the atomic number
The number of protons in an atom is what gives an atom its identity
Carbon will always have 6 protons Atomic number = 6 Neon will
always have 10 protons Atomic number = 10 The atomic number is on
the periodic table and is used to identify each element Atomic
Number
- Slide 10
- The nucleus contains most of the mass of an atom The mass of a
proton and a neutron are very similar 1.67 x 10 -24 g The mass of a
proton (or a neutron) is 1,836 times greater than that of an
electron Because the mass of proton or neutron is awkward to use, a
standard measurement is used. Each proton or neutron has a mass of
approximately 1 atomic mass unit (1 amu) Carbon has 6 protons and 6
neutrons 6(1) + 6(1)= 12 amu (mass of a carbon atom) Why didnt we
use the mass of an electrons? Atomic Mass
- Slide 11
- The mass number of an atom is the sum of the number of protons
and neutrons Remember: This is because each proton or neutron has a
mass of 1 amu If you know the mass number and the atomic number of
an atom, you can determine the number of neutrons # of Neutrons =
Mass Number Atomic number Example: How many neutrons are in an
Carbon atom that has a mass number of 14? What is the atomic number
of Carbon? 6 14 6 = 8 There are 8 neutrons in the atom. Mass
Number
- Slide 12
- All atoms of an element will have the same number of protons
But not all the atoms will always have the same number of neutrons
Atoms of the same element that have different numbers of neutrons
are called isotopes Isotopes are usually identified by their mass
number Carbon-12 (6 protons, 6 neutrons) Carbon-14 (6 protons, 8
neutrons) Boron-10 (5 protons, 5 neutrons) Boron-11 (5 protons, 7
neutrons) How many neutrons does Oxygen-18 have? Isotopes
- Slide 13
- Because not all the atoms of an element have the same mass, an
average mass is used To figure out the average mass, we need to
know how many of each isotope is present in a sample Scientists do
this by using weighted averages For example: 80% of all Boron atoms
are Boron-11 20% of all Boron atoms are Boron-10.80(11) +.20(10) =
10.8 amu Average Atomic Mass