The Nature of Matter
Chapter 1

Inside the Atom

Models of the Atom

•      Greek philosophers devised a theory of atoms, or tiny particles

•      They couldn’t perform experiments and collect evidence like we do now

–    They reasoned and formed conclusions

•      They reasoned that if you keep cutting matter in half, you would eventually not be able to cut it anymore

–    They called these particles atoms

John Dalton

•      He was a school teacher in England (early 1800s)

•      Dalton combined the idea of elements with the Greek theory of the atom

•      Matter is made up of atoms

•      Atoms cannot be divided into smaller pieces

•      All atoms of an element are exactly alike

•      Different elements are made of different atoms

William Crookes

•      Crookes tested Dalton’s theory using a cathode-ray tube

–    Almost all air removed

–    Two pieces of metal called electrodes (conduct electricity) sealed inside and connected to a battery by wires

–    He placed a cross-shaped object between the electrodes

•      When he connected the battery, the glass tube lit up with a greenish glow

•      On the positive side, there was a shadow of a cross.

•      Something was traveling from the negative side to the positive side and was being blocked by the cross

J. J. Thomson

•      Thomson (1897, England) placed a magnet by the cathode ray tube and discovered he could move the cathode rays. 

•      He also used different metals and gasses and discovered that there are negatively charged particles (electrons) in every atom

•      Thomson revised Dalton’s model to include a sphere with a positive charge and negatively charged electrons spread evenly within the positive charge

•      The negatively charged electrons and the positive charge in the sphere neutralized each other

Earnest Rutherford

•      Rutherford tested Thomson’s model in 1906

•      His team fired fast-moving, positively charged bits of matter (alpha particles) at a thin film of metal (gold was mainly used)

•      If Thomson’s model were true, there isn’t enough charge anywhere in an atom to repel an alpha particle and they would go straight through the thin film of metal

–    Occasionally on alpha particle would come directly into contact with a positive charge and be repelled, but not often

Earnest Rutherford – The Reality

•      When the alpha particles were fired, many bounced off at large angles

•      Rutherford said, “It was about as believable as if you had fired a 15-inch shell at a piece of tissue paper, and it came back and hit you.”

•      There had a to be a large positive mass somewhere to deflect the alpha particles

•      Thus, Thomson’s model could not be correct

A New Atomic Model

•      The idea of a nucleus was developed

–    Rutherford said that almost all of the mass of an atom must be in the center (nucleus) and must be positively charged

–    In 1920, scientists identified the positive charges in the nucleus as protons

•      Most of an atom is empty space occupied by nearly massless electrons

•      Electrons orbit the nucleus and the number of electrons equals the number of protons in a stable atom

A New Atomic Model

•      Since electrons have no mass and there are no other particles, the mass of an atom must equal the number of protons

•      The mass of atoms, however, is at least twice that of the number of protons

•      It was proposed that another particle must be in the nucleus

•      Later called the neutron and discovered to have almost the exact mass of a proton and no charge

How Big is an Atom?

•      An atom is to an apple as an apple is to the ________?

•      The moon

•      An atom is to me as I am to the _______.

•      The sun

•      There are as many atoms in one breath as there are breaths in the ____________.

•      Atmosphere

Electron Shells

•      This is simplified method of explaining the orbits of electrons

•      There are “shells” around the nucleus kind of like different orbits around a planet.

•      Each shell can hold a different amount of electrons:

–    Shell #1 – 2 electrons

–    Shell #2 – 8 electrons

–    Shell #3 – 18 electrons (or 8)

–    Shell #4 - 32 electrons (or 8)

•      Not a realistic explanation of how electrons orbit the nucleus

•      If an atom were a golf ball, shell #1 would be 1 km away

The Electron Cloud Model

•      The electron cloud model explains the unpredictable wave behavior of electrons, which could be anywhere in the area surrounding the nucleus

•      These clouds are often referred to as electron orbitals

Orbitals

•      There are four different shapes of orbitals corresponding to 4 letters:

–    s (holds up to 2 electrons)

 

 

–    p (holds up to 6 electrons)

Orbitals

•      d (holds up to 10 electrons)

 

 

 

•      f (holds up to 14 electrons)

Orbitals

•      DON’T WRITE THIS DOWN!

•      The orbital closest to the nucleus is the 1s orbital and it can hold 2 electrons

•      The 2s is next and can hold two more.  Then there is a 2p orbital that can hold 6 more electrons.

•      Then comes a 3s (2), 3p (6) and a 3d (10), 4s (2), 4p(6), 4d (10), and 4f (14)

•      But this method is also screwed up. In actuality, the orbitals fill up in this order:

–    1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 5d, 4f, 6p, 7s, 6d, 5f, 7p (or something like that – you don’t need to remember it for sure)

 

The Elements

•      Elements are materials that cannot be broken down into simpler materials without becoming a different kind of atom

•      As of 2002, there were 115 known elements (your agenda only has 114)

–    90 are naturally occurring

–    25 are synthetic elements (made in a laboratory)

•      4 most common elements in life:

–    Carbon, Hydrogen, Oxygen, Nitrogen

•      4 most common elements in the Earth

–    Oxygen, silica, aluminum, iron

The Periodic Table

•      The Periodic Table is a chart that organizes and displays information about the elements

•      The elements represented by the symbols on the periodic table are placed purposely in their position on the table

•      Even the shape of the periodic table is that way on purpose

 

The Periodic Table

•      The rows are called periods

–   They have the same number of energy levels (1 in the 1s, etc.)

•      The columns are called groups

–   They have similar properties and tend to form similar bonds

Atomic Number

•      The atomic number is the top number in the element’s periodic table block

•      Tells the number of protons in the nucleus of each atom of an element

–    Also the number of electrons in an electronically neutral atom

•      The number of protons remains constant in every atom of an element

Isotopes and Ions

•      Isotopes are atoms of the same element that have different numbers of neutrons

•      Ions are atoms of the same element that have different numbers of electrons

–    Except for the elements in Group 18, all atoms have an empty spot in their outermost electron orbital and “nature” hates this

–    So atoms either lose or gain electrons to fill these spots

Mass Number and Atomic Mass

•      Mass number is the number of protons plus the number of neutrons (different mass numbers for different isotopes)

•      Atomic mass is the average mass of all the isotopes of an element

•      The atomic mass is found below the element symbol

•      The unit used for atomic mass is the atomic mass unit, or “u”

Calculating Neutrons

•      To find the number of neutrons in the MOST COMMON isotope of an atom:

–    (Rounded atomic mass) - (atomic number)

•      So how many neutrons are in Helium?  Sulfur?

Metals

•      The majority of elements are metals (blue in your book)

•      Metals have a shiny luster

•      Good conductors of heat and electricity

•      Solids at room temperature

•      Malleable (can be shaped)

•      Ductile (can be drawn into wires without breaking)

Nonmetals

•      Nonmetals are found on the right side of the periodic table (yellow in your book)

•      Dull luster

•      Poor conductors of heat and electricity

•      Many are gases at room temperature

•      Brittle (cannot change shape without breaking)

•      96% of the human body is made up of nonmatals

Metalloids

•      Metalloids are found between the metals and nonmetals on the periodic table (green in your book)

•      Have characteristics of both metals and nonmetals

•      Do not conduct heat and electricity as well as metals

•      All are solids at room temperature

 

Substances

•      Matter that has the same composition and properties throughout is known as a substance.

Molecules

•      A molecule is a group of atoms that are bound tightly together by sharing electrons

•      It’s also the smallest unit of a substance that shows all the chemical properties of that substance.

–    Ex: one water molecule

Compounds

•      A compound is a substance whose smallest unit is made up of atoms of more than one element (can be a molecule)

•      Written in formulas

–    The subscript number tells how many atoms of the preceding element are in the compound

_•     Ex: CO₂

–    No subscript is used when only one atom of the element is present

•    Ex: HCl

•      A given compound is always made of the same elements in the same proportion

–    Ex:  Water is always H₂O, never HO₂ or H₃O

Mixtures

•      Mixtures occur when two or more substances mixed together which don’t make a new substance

•      Unlike compounds, the proportions of the substances can be changed

•      Examples:  air, blood

•      Mixtures can be separated easily

•      Homogeneous mixtures are the same throughout the whole mixture

–    Ex: Kool-aid, soup broth

•      In heterogeneous mixtures, you can see the different parts

–    Ex: most rocks, tacos