Chapter 1: introduction to the atom

UNDERSTANDING ATOMS

• 100 different types of atoms

-properties are determined by arrangement of atoms

• Joseph J. Thomson: experimented to determine the ratio of an electron’s mass to charge

•Robert Milikan: Determined charge of electron

• all matter is composed of atoms

• atom - the smallest part of an element that is still that element

• molecule - two or more atoms joined and acting as a unit

• diatomic molecules are chemicals that naturally possess 2 atoms:

-H2, O2, N2, F2, Cl2, Br2, and I2

A CHEMICAL REACTION

• one substance changes to another by reorganizing the way the atoms are attached to each other

- going from left —> to right is favored reaction

FUNDAMENTAL LAWS

• law of conservation of mass - mass is neither created nor destroyed in a chemical reaction

• law of definite proportion - a given compound always contains exactly the same proportion of elements by mass (earlier known as Proust’s Law, determined by weighing various elements in compounds)

-ex. table salt from cali and salt from boston will have the same exact mass, because sodium chloride is ALWAYS NaCl

- constancy in chemical formulas

DALTON’S ATOMIC THEORY

• each element is made up of tiny particles called atoms

• (MISSED)

• chemical reactions involve reorganization of the atoms changes in the way they are bound together

• prepared the first table of atomic masses

- also called atomic weights

- some of the masses were not accurate because there were not correct formulas for all compounds back then

• elements are made of tiny particles called atoms

• a given compound always has the same relative numbers and types of atoms

• atoms are NOT indestructable

- can be split into protons, neutrons, and electrons.

COMPOSITION OF AN ATOM

• protons: found in nucleus

• electrons: found outside nucleus

• neutrons: found in the nucleus

• an atom is mostly empty space

- still extremely minuscule

• the nucleus is very small and dense in the center of the atom

MASS DEFECT STABILITY OF A NUCLEUS

• • neutrons, protons, electroms come together and the mass of the formed atom is less than the component masses of the protons, neutrons, and electrons

• • ∆E = ∆mcˆ2 can explain this

- when a system loses or gains energy, it also loses or gains a quantity of mass, given by ∆E/cˆ2

- ∆m is the change in mass or Mass Defect

- ∆E is the binding energy

- c is the speed of light (constant)

ALL ATOMS HAVE THE SAME COMPONENTS BUT DIFFERENT PROPERTIES

• determined by # of electrons and arrangement of electrons

• e- of different atoms intermingle to form molecules

ISOTOPES

• isotopes: atoms with the same number of protons but different numbers of neutrons

- protons + neutrons: mass #

- atomic # does not change, and protons stay the same

• element with atomic # of 9 and mass # 19

-indicator is the atomic # - goes in order on periodic table

- Fluorine

- 19-9 = 10 neutrons, 9 protons

ISOTOPIC ABUNDANCE

* average atomic mass of all atoms of an element is calculated using: ∑(fractional abundance x isotopic mass)

• Ex: Bromine has 2 naturally occurring isotopes. One with a mass of 78.918336 amu (u) and an abundance of 50.69%. The other isotope has a mass of 80.916289 amu, has an abundance of 49.31%.

Calculate the average atomic mass of bromine.

ASSIGNING A CHARGE TO AN ATOM: ION

• number of protons in a neutral atom and number of electrons are exactly the same

• ions are formed when the “neutrality” is disturbed

• atom loses an e- —> residual charge of the atom will be +

- known as a positive ion or cation

- electron will always leave from the outer ring because it is energetically more favorable: - ionization energy: energy used to remove electron from atom

• ionization equation to form positive ions:

Na —> Na+ + e-

- positive charge and negative  charge have to be balanced

- e- is a product so it has to be on the right

* positive ions are smaller because of the lost electron(s)

• group # correlates to the # e- given

- ion size decreases as you go from left —> right on the periodic table

• when a negative ion forms an electron is added

- known as anions

- atom has an electron affinity

- adding electrons to outer orbitals increases the size of the ion compared to the neutral atom.

REVIEW OF PERIODIC TABLE:

Alkali metals: group 1

Alkaline earth metals: group 2

transition metals: 3-12

main group elements: 1-2 and 13-18

• many of the elements pulled out of the table are radioactive and have similar properties

* metals on the left-hand side

- strong conductors of electricity

• non-metals on the right-hand side (15-18)- do not conduct electricity

• metalloids -  along the zigzag line separating metals and non-metals -semiconductors have properties not quite like metals and not quite like non-metals, ex: silicon