Atomic Structure 3.1

Atomic History In 400 BC a Greek Philosopher named Democritus suggested the universe was made of invisible units called atoms.

1800’s John Dalton’s Theory (Still Accepted) Every element is made of tiny, unique particles called atoms Atoms of different elements can join to form molecules.

John Dalton’s Theory- Disproved Atoms are the smallest particles and cannot be subdivided. Atoms of the same element are exactly alike in mass

JJ Thomson Credited with discovering negative charged particles called electrons.

Rutherford Credited with discovering the nucleus. Also concluded that atoms are mostly empty space.

http://micro.magnet.fsu.edu/electromag/java/rutherford/

Further Research Finding Later on, the discovery of protons and neutrons were discovered in the nucleus. And it was later concluded that all atoms are neutral in charge. The number of protons and electrons in any atom are always equal.

Niels Bohr Suggested that electrons move around atoms in set paths around the nucleus. He said each path is an energy level

Today’s Theory It has been determined that it is impossible to pinpoint an electron’s exact position due to its tremendous speed. Electrons do not move around in definite paths.

Today’s Theory Electrons are found in orbitals within energy levels. (s, p, d, and f ) a region in an atom where there is a high probability of finding electrons.

Today’s Theory Electrons are now viewed as waves vibrating on a string rather than simple particles. Wave-Particle Duality Theory

What are atoms? The smallest part of an element that still has the element’s properties.

Parts of an atom Nucleus Proton Neutron Electron Subatomic particles

Nucleus center of an atom positively charged makes up 99.9% of the atom’s mass contains protons and neutrons

Protons Charge (+) Mass is equal to 1 atomic mass unit (amu) Found in the nucleus Identifies the element/atom

Neutrons Charge (0) – neutral Mass is equal to 1amu Found in the nucleus Helps determine mass

Electrons Charge is negative (-) Mass is equal to 0 amu Found outside the nucleus, in the electron cloud

Energy levels 1st level holds up to 2 e- 2nd level holds up to 8 e- 3rd level holds up to 8 or 18 e- 4th level holds up to 8, 18, or 32 e- Outer Level holds up to 8 e- (called valence electrons)

Valence Electron The number of electrons in the outermost electron shell. Most important

A Guided Tour of the Periodic Table 3.2

Periodic Law Properties of elements tend to change in a regular pattern when elements are arranged in order of increasing atomic number.

Periodic Table is set up by increasing atomic number. Periodic Law Periodic Table is set up by increasing atomic number. Atomic Number is the # of protons in the atom.

Average Atomic Mass

tells you number of protons Never Changes for an atom. Atomic Number tells you number of protons Never Changes for an atom. Appears as a whole # on the periodic table. No two elements can have same atomic #.

Atomic Number Atomic Number # of protons

Total number of protons plus neutrons in the nucleus of a single atom. Mass Number The mass of an atom Total number of protons plus neutrons in the nucleus of a single atom. Atoms of the same element won’t always have the same mass number

Mass Number # of neutrons Mass # # of protons

So they also have different mass numbers. Isotopes Any atoms having the same number of protons but different number of neutrons. So they also have different mass numbers.

Average mass of all known isotopes for an element Average Atomic Mass Average mass of all known isotopes for an element Found on the periodic table as a number with a decimal

All atoms have the same number of protons and electrons. Atom’s Charge They are neutral. All atoms have the same number of protons and electrons. Charges cancel each other out.

Form when atoms lose or gain electrons. Ions Charged particles. Form when atoms lose or gain electrons. They do this so the ions have a full outer shell Two Types.

Positively charged ions. Form when atoms lose electrons. Metals Cations Positively charged ions. Form when atoms lose electrons. Metals Left side of table

# of protons greater than # of electrons More (+) than (-) Cations # of protons greater than # of electrons More (+) than (-)

Na Atom Na+ Cation

Negatively charged ions. Form when atoms gain electrons. Nonmetals Anions Negatively charged ions. Form when atoms gain electrons. Nonmetals Right side of table

# of protons less than # of electrons More (-) than (+) Anions # of protons less than # of electrons More (-) than (+)

Cl- Anion Cl atom

Quantifying atoms or ions +1 Protons = 3 Neutrons = 7-3 = 4 Electrons = 3 Electrons = 3 -1 = 2

Families of Elements 3.3

Periodic Table Periods -a horizontal row of elements. -Tells you the electrons energy level.

Periodic Table Groups (families) -a vertical column of elements. -Tells us the # of valence electrons and the elements’ chemical properties.

Semiconductors/metalloids Types of Elements Metals Nonmetals Semiconductors/metalloids

Inner Transition Metals Alkali Metals Nobel Gases Non Metals Alkaline Earth Metals Metalloids Halogens Other Metals Transition Metals Inner Transition Metals

Alkali Metals Group 1 Most reactive metals one valence e- Found as compounds (salts) and not elements due to reactivity. As elements they are soft metals and good conductors.

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Alkaline-earth Metals Group 2 Less reactive than Alkali They are also more commonly found as compounds 2 most common are Ca and Mg.

Transition Metals Groups 3-12 Less reactive than groups 1 and 2 Good conductors

Transition Metals All solids with the exception of mercury Valuable metals (Ag, Au, Pt, Cu, Ni, Fe, Co)

Non Metals Are not able to conduct electricity or heat very well. Found in groups 13-18, with the exception of hydrogen

Carbon Found as an element (coal, diamond, graphite) Found in millions of different compounds Called Organic Compounds

HYDROGEN It is a gas/nonmetal A very explosive gas. It is located in group one because it has one valence electron http://video.google.com/videoplay?docid=- 2380118142773657669&q=hindenburg&hl=en

Oxygen is the most common element found on Earth Oxygen and Nitrogen Oxygen is the most common element found on Earth Nitrogen most common gas found in the atmosphere

Halogens Group 17 Most reactive nonmetals Form salts with group 1 Used to kill bacteria Bromine only liquid nonmetal

Noble Gases Group 18 Stable and not reactive. (inert) Don’t form compounds. They have a full valence shell.

Metalloids (Semiconductors) 7 elements on the step Properties of both metals and non- metals. Silicon the most familiar (computer chips)

Inner Transition Metals Two rows at the bottom Some are Radioactive ex. Uranium 93 and greater are all manmade

Moles 3.4

Counting Units We buy things by the dozen. One dozen = 12 items We use the unit mole to count things in chemistry

Moles the SI base unit that describes the amount of a substance.

Avogadro’s Constant Represents the number of particles in one mole of a substance. The number is 6.02 x 1023 particles, atoms, or molecules

Moles Used for counting with really tiny atoms One mole represents the atomic mass of an element.

Molar Mass The mass in grams of 1 mol of a substance. Using the periodic chart you can determine the molar mass of any element or compound.

Molar Mass Example So how many grams in two moles of Ca?

Solution The molar mass of Ca is 40 g/mol. 2 moles x 40 grams = 80 g

Mole Problems You can determine how many moles of a substance you have if you know the mass of the substance.

Example Problem If you have 92 grams of Na how many moles would you have?

Solution MM of Na is 23 g/mole 92 g x 1 mole = 4.0 moles 23 g