ATOMIC STRUCTURE

AND ELECTRON

CONFIGURATION

CHAPTER THREE

PAGE 73

LET’S READ SOMETHING TO THINK ABOUT!!!!

EXCITED ATOMS AND THE FOURTH OF JULY!!!!!

Dalton's Atomic Theory

1) All matter is made of atoms. Atoms are indivisible and indestructible.

2) All atoms of a given element are identical in mass and properties

3) Compounds are formed by a combination of two or more different kinds of atoms.

4) A chemical reaction is a rearrangement of atoms.

Law of definite proportions

Sometimes called Proust's Law, states that a chemical compound always contains exactly the same proportion of elements by mass. An equivalent statement is the law of constant composition, which states that all samples of a given chemical compound have the same elemental composition by mass. For example, oxygen makes up about 8/9 of the mass of any sample of pure water, while hydrogen makes up the remaining 1/9 of the mass.

LAW OF CONSERVATION OF MASS

Definition: Law of Conservation of Mass is a relation stating that in a chemical reaction, the mass of the products equals the mass of the reactants.

DEFINITION OF MULTIPLE PROPORTIONS

two elements can combine to form more than one compound, the ratio by weight of one element to a given weight of the second is usually a small whole number

EXAMPLES: NO2, NO, N2O or H2O, H2O2.

ATOMIC MASS: The simplest explanation for what is

atomic mass unit is that it is equal to 1/12 of a carbon 12 atom. You might see an atomic mass unit called by it's other name--a dalton.

MOLE - SI unit for amount

AVOGADRO’S CONSTANT: the number of particles, 6.022 X 10 23, in exactly 1 mole of a pure substance.

PARTS OF AN ATOM

NUCLEUS – Gold Foil ExperimentProtons - positively charged

particlesNeutrons – neutrally charged

particles

ELECTRON CLOUD – Cathode Ray TubeElectrons – Negatively charged

particles

WHAT IS THE INTERNAL STRUCTURE OF ATOMS?

ELECTRON

J. J. Thomson was born in a suburbof Manchester, England, in 1856.He studied mathematics at Trinity College and became a professor there. His pioneering research into the nature of cathode rays led to his discovery of the electron. He won the Nobel Prize in physics in 1906, and was knighted in 1908. He diedin Cambridge in 1940.

J J Thomson Research – ElectronIn 1894, Thomson began studying cathode rays, which

are glowing beams of light that follow an electrical discharge in a high-vacuum tube. It was a popular research topic among physicists at the time because the nature of cathode rays was unclear.

Thomson devised better equipment and methods than had been used before. When he passed the rays through the vacuum, he was able to measure the angle at which they were deflected and calculate the ratio of the electrical charge to the mass of the particles. He discovered that the ratio was the same regardless of what type of gas was used, which led him to conclude that the particles that made up the gases were universal. He determined that all matter is made up of tiny particles that are much smaller than atoms. He originally called these particles 'corpuscles,' although they are now called electrons. This discovery upended the prevailing theory that the atom was the smallest fundamental unit.

J J Thomas’s Cathode Ray Experiment Setup

Ernest Rutherford

was born on August 30, 1871, in Nelson, New Zealand, the fourth child and second son in a family of seven sons and five daughters. His father James Rutherford, aScottish wheelwright, emigrated to New Zealand with Ernest's grandfather and the whole family in 1842. His mother was an English schoolteacher, who, withHer widowed mother, also went to live there in 1855.Ernest received his early education in Governmentschools and at the age of 16 entered Nelson Collegiate School. In 1889 he was awarded a University scholarship and he proceeded to the University of New Zealand, Wellington,where he entered Canterbury College*. He graduated M.A. in 1893 with a double first in Mathematics and Physical Science and he continued with research work at the College for a shorttime, receiving the B.Sc. degree the following year. That same year, 1894, he was awarded an 1851 Exhibition Science Scholarship,

Before Ernest Rutherford's landmark experiment with a few pieces of metal foil and alpha particles, the structure of the atom was thought to correspond with the plum pudding model. In summary, the plum pudding model was hypothesized by J.J. Thomson (the discoverer of the electron) who described an atom as being a large positively charged body that contained small, free-floating, negatively charged particles called electrons. The plum pudding model also states that the negative charge of the electrons is equivalent to the positive charge of the rest of the atom. The two charges cancel each other causing and cause the electrical charge of the atom to be zero (or neutral). The faulty aspect of this model is that it was construed before the nucleus of an atom (and its composition) was discovered; which is where Rutherford's research comes in.

Atomic Number:The number of protons in nucleus

Mass Number:The number of protons plus the

number of neutrons

Isotopes:Atoms of the same element with different numbers of neutrons

SYMBOLS CAN REPRESENT ATOMIC SRUCTURES

Each element has a name and each atom of that element has the same name.Example: oxygen is composed of oxygen

atoms Each element has a symbolExample: O represents oxygen

To indicate numbers of atoms scientist use subscriptsO2 two atoms of oxygen

Atomic number and mass number are sometimes written with an element’s symbol; sometimes indicating isotopes : page 88

Coulomb’s Law: The closer two charges come

together, the greater the force between them.

If the charges have different signs, they attract one another. If the charges are alike, they repel one another.

Strong Force- helps overcome repulsion of same sign particles at close distances. Hence, protons and neutrons can form

stable nuclei by strong forces.

ISOTOPES ATOMS OF THE SAME ELEMENT WITH

DIFFERENT NUMBERS OF NEUTRONS Helium-3 Helium-4

Number of protons always the same

Number of electrons-always the same

Number of neutrons differ

atomic mass (decimal number on Periodic table)

LET’S TRY IT

PAGE 90

Section Review:1, 2, 3, 5, 7

ELECTRON CONFIGURATIONS

•electromagnetic wave: example Light•Three parts to these waves:

speed, wavelength, frequencySpeed- speed of light : 2.998 X 108 m/s. (с)Wavelength- distance between two

consecutive peaks or troughs in a wave. ( )Frequency- number of waves that pass a

stationary point.( γ ) frequency x wavelength = speed of light

Page 95: Figure 3-23

GROUND STATE- lowest energy state of quantized energyEXCITED STATE- atom in a higher

energy stateQUANTUM NUMBER- a number with certain definite values.ORBITALS- a region of an atom in

which there is a high probability of finding one or more electrons.

s, p, d, f

QUANTUM NUMBERS

n = principal quantum numberenergy level- 1,2,3,4,5,6,7larger the number- farther the orbit is

out

l = indicates orbit e- is located, n→ n−1 so if n=1, then l=0 or 1.

l = 0 corresponds to s orbitall = 1 ῎ ῎ ῎ p orbitall = 2 d orbitall = 3 f orbital

m = dependent on l quantum number whole number valuel = 1 then m = -1, 0, 1 ( p orbital)l = 2 then m = -2, -1, 0, 1, 2 (d orbital)

l and m quantum numbers designate the shape and the orientation of the orbitals

ms = spin quantum number, +1/2 or -1/2

Quantum theory tells us exact energy of the e-, but only the probability that the e- will be in that particular region.

Page 98 in text shows shapes of orbitals Pauli’s exclusion principle- up to two e- can

occupy the same orbital . If 2 e- do occupy the same orbital, they must have different spins.

Aufbau Principle- German word for “building up”

e- fill the lowest energy orbitals first

We know: which orbitals are occupied by how many e-

This tells us the electron configuration of an atom.

ELECTRON CONFIGURATIONS

1. Determine the total number of electrons an atom possesses.2. Fill orbitals in order of increasing energy.3. Make sure the total number of electrons in the electron configuration equals the atomic number. *as long as it’s not an ion

Let’s try a few!!!!!Sc, K, P, B, In, Ba

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