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ATOMS: THE BUILDING
BLOCKS OF MATTER
Ms. Moore Chemistry
THE ATOM
• Democrites- described natures particles as an atom( indivisible)
• Three laws to describe behavior of matter
• 1) The law of conservation of matter- states that matter can neither be created
nor destroyed during chemical reactions or physical change.
• 2) The law of definite proportions- a chemical compound contains the same
elements in exactly the same proportions by mass regardless of the size of the
sample or the source of the compound.
• 3) The law of multiple proportions- if two or more different compounds are
composed of the same two elements, then the ratio of the masses of the second
element combines with a certain mass of the first element is always a ratio of
small whole numbers.
LAW OF MULTIPLE PROPORTIONS
DALTON’S ATOMIC THEORY
• Elements are made of small, indivisible particles called
atoms
• Atoms of an element are identical and have the same mass
and properties
• Atoms combine to form compounds in small, whole # ratios
• Chemical Reactions are the rearrangement of atoms
STRUCTURE OF THE ATOM
• Atoms contain positive and negative particles
• JJ Thompson proved that electrons existed by using a cathode ray tube
• 1) Cathode rays were deflected by a magnetic field in which a wire carrying
electrical current is known to have a negative charge
• 2) The rays were deflected away from a negatively charged object.
• He measured the ratio of the charge of cathode-ray particles to their mass. And
found the ratio to be the same regardless of the metal.
• -Named the particle electrons
• https://www.youtube.com/watch?v=2xKZRpAsWL8
• Milikans oil drop experiment- https://www.youtube.com/watch?v=XMfYHag7L
 Millikan’s Oil Drop Experiment
 Showed that if a drop of oil were exposed to X- Rays, it
became charged from the air
 By having the drop fall between two electrical plates
◦ Determined the average mass of a drop
◦ Drop was suspended in air using the electrical field
◦ By knowing what field was necessary to hold the drops, he was
able to determine the charge
 1.602 x 10-19 Coulombs
Media Resources\Rutherford Gold Foil.mov
• Rutherford’s Gold Foil Experiment
MODERN ATOMIC STRUCTURE
• Nucleus
• Protons – large, positively charged particle
• Neutron – large, neutrally charged particle
• Electron – small, negatively charged particle
Particle
Relative Mass
Relative Charge
Electron
1
-1
Proton
1836
+1
Neutron
1836
0
ISOTOPES
• Atoms of an element must have the same # of protons
• Atomic Number (Z) – number of protons
• Atoms of an element can have a different # of neutrons
• Mass Number (A) – sum of protons and neutrons
• Atoms of an element can have a different # of electrons
• Charge = (Protons – Electrons)
• Mass Number- is the total number of protons and neutrons that make up the
nucleus of an isotope.
• Mass number= Protons + neutrons
• Atomic Number= number of protons= number of electrons.
• Ex: how many protons electrons and neutrons are there in an atom of chlorine
37?
• 1) The atomic number found on the periodic table is equal to the number of protons.
• 2) The number of protons equals the number of electrons.
• 3) The mass number=( protons + neutrons)- the atomic number equals the number of
electrons.
PRACTICE
• How many protons, electrons , and neutrons make up an atom of bromine80?
• 35 protons 35 electrons and 45 neutrons
• Write the nuclear symbol for Carbon 13
• Write the notation for the isotope 15 electrons and 15 neutrons.
• Phosphorous 30
CHARGED ISOTOPES
• If the isotope is charged such as 37 Cl -1 add the charge to the number of
protons to get a total number of electrons.
•
P:
17 N: 20 E: 18 therefore making the isotope have a charge of negative 1
WEIGHTED ATOMIC MASS
• The weighted average of the atomic masses of the naturally occurring
isotopes of an element.
• 1) convert the percentage to decimal form
• 2) multiply the relative abundance by the atomic mass of each isotope.
• 3) add up each result
• Ex: What is the atomic mass of Chlorine?
• 35Cl: 75.77% 34.969 amu
• 37Cl: 24.23% 36.966 amu
• .7577 ∗ 34.969 + .2423 ∗ 36.966 = 35.46
ELECTRON CONFIGURATION
PERIODIC TABLE
PERIODIC TABLE
• Developed by Mendeleev in 1869
• Placed elements in groups (columns) based on their properties
• Group (Family)
• Vertical column of elements
• Strongly related by properties
• Period (Row)
• Related by a systematic change in properties
• Alkali Metals
GROUPS
• 1st column
• Highly Reactive
• Reactivity Increases down the table
• Never found naturally in the pure state
• Na found as Na+…K as K+
• Soft, Low Densities
• React with H2O to make Base
2 Na( s)  2 H2 O(l )  2 NaOH (aq)  H2 ( g)
ALKALI METALS
• Alkaline Earth Metals
GROUPS
• 2nd Column
• Reactive, but less than Alkali Metals
• Reactivity increases down the Periodic Table
• Never found naturally in pure state
• Soft, but harder than Alkali Metals
• React with H2O to make Base
Mg( s)  2 H2 O(l )  Mg(OH ) 2 (aq)  H2 ( g)
ALKALI EARTH METALS
• Next to Last column
HALOGENS
• Highly reactive non-metals
• Reactivity increases UP the Periodic Table
• Rarely found naturally in the pure state
• Powerful oxidizing agents
• Gases, Liquids and Solid
• Colorful compounds in pure state
• Combine with Hydrogen to make Acids
• HF, HCl, HBr, HI
H2 ( g)  Cl2 ( g)  2 HCl ( g)
HALOGENS
NOBLE GASES
• Last Column
• Almost completely non-reactive gases
• Very Few compounds exist
• Melting points and Boiling points differ by less than 10
ºC
• Argon is 1.3% of air (by mass)
• Discovered and obtained from fractional distillation
of air
NOBLE METALS
• Very non-reactive metals
• Highly resistant to corrosion or oxidation
• Found naturally in the pure state
• Copper, Silver, Gold
• Clean surfaces in a vacuum stay clean
• Many lists include other metals
• Especially Platinum & Palladium
• Both of these will have a dirty surface quickly (CO)
• Properties
• Good conductors of heat and electricity
• Shiny surface (high luster)
• Malleable
• Ductile
• Found on the left side of the table
• Solids at Room Temperature
• Most elements on the Periodic Table
METALS
NON-METALS
• Properties
• Poor conductors (heat and electricity)
• Colorful substances in the pure state
• Many gases and a few soft solids
• Found on the extreme right side of the table
SEMIMETALS
• Also called metalloids
• Properties are between metals and non-metals
• Stair-step of elements that separate the two main types
• Everything to the left of the stair step
• Metal
• Everything to the right of the stair step
• Non-metal
OTHER GROUPS
• Main Group
• Elements in 1st two and last 6 columns
• Make up the most abundant elements
• Transition Metals
• Center Block of metals (called “d-block”)
• Inner Transition Metals
• Block at the bottom of the table (“f-block”)
SUMMARY
Metals
Non-metals
NATURAL STATES
• Most of the elements are found as a solid when pure (“standard state”)
• Liquids
• Mercury, Bromine
• Gallium has a very low melting point (29.8 ºC)
• Gases
• Noble Gases
• Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine
ELEMENTS
• Pure elements are not always individual atoms
• Diatomic Elements – elements which are always found pure as a bonded pair of
atoms
•
•
•
•
•
•
•
Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Fluorine (F2)
Chlorine (Cl2)
Bromine (Br2)
Iodine (I2)
ALLOTROPES
• Pure substances found naturally in different forms of the same physical state
• Carbon – 40+ known allotropes
• Graphite – chemically stable
• Flat sheets of carbon
• Diamond – chemically unstable
• 3-D bonded structure
• Extremely hard and strong
• 1 giant molecule
• Buckminster Fullerene
• C60 – soccer ball structure (pentagon/hexagon)