Chapter 5Chapter 5

Atomic Structure and The Periodic Table

Early Models of the Atom

• John Dalton ( 1766-1844) An English School teacher

• He studied the ratios in which elements combine in chemical reactions

• Daltons Atomic Theory:

1. All elements are composed of tiny particles called atoms

and

2. Atoms of the same elements are identical. Those atoms of one element are different from those atoms of another element

(Pg. 107 in book)

Just How Small is an Atom?Just How Small is an Atom?

• Atom: the smallest particle of an element that still has the same properties of that element

• Copper atoms are very small, for example, if you could line up 100 000 000 copper atoms side by side it would make a line 1 cm long

• Even though atoms are this small you can still see and move them around with a scanning tunneling microscope

                              

ElectronsElectrons

• Negatively charged subatomic particles

• In a cathode-ray tube, electrons travel as a ray from the cathode (-) to the anode (+). A television tube is a specialized type of cathode-ray tube.

The green balls are electrons orbiting the nucleus

The ic NucleusThe ic Nucleus

• The atom was mostly empty space • The nucleus: is the central core of an atom and it

made up of protons and neutrons • The nucleus is tiny compared to an atom as a

whole• Rutherford suggested this new theory of an atom

Atomic NumberAtomic Number

• Atomic numberAtomic number- the number of protons in the nucleus of an atom of a element

• The atomic number identifies an element

• Hydrogen has 1 proton, so its atomic number is 1

• When the number of protons is equal to the electrons, this atom is neutral because it has equal positive and negative charges

• Not until the atom loses or gains an electron does it become either negative if it gains an electron or positive if it loses an electron

Protons and NeutronsProtons and Neutrons

• Protons- positively charged subatomic particles• Neutrons- subatomic particles with no charge • Protons and neutrons have nearly the same mass• Protons and Neutrons are found in the inside of an

atoms with electrons orbiting them

mass  charge 

protons approx. 1 amu +

neutrons approx. 1 amu 0

electrons   1/1800 amu  -

MASS NUMBERMASS NUMBER

• Mass number: number of protons and neutrons in an atom

• Number of Neutrons = mass number – atomic number

• The composition of any atom can be represented by the atomic mass and the mass number

Atomic MassAtomic Mass• Atomic Mass: is a weighed average mass of the

atoms in a naturally occurring sample of the element

• Atomic Mass Unit (amu): one twelfth the mass of a carbon-12 atom

                                                                                   

                                  

Isotopes: Atoms of the same element that have the same number of protons but

different number of neutrons ; pg. 119

Isotope Information

• All isotopes of an element “act” the same as they move through “systems”

• Most elements have at least one radioactive isotope. This can be “traced” see pg. 859-861

• The atomic mass on the periodic table is the average of all isotopes for that element…the most common element is the one closest to the mass on the periodic table.

• Uses of radioactive isotopes: 1. To diagnose a problem 2. Chemotherapy The reason: some elements tend to accumulate in specific regions of the body

• Chemotherapy• Chemotherapy is a systemic therapy; this means it affects the whole

body by going through the bloodstream. The purpose of chemotherapy and other systemic treatments is to get rid of any cancer cells that may have spread from where the cancer started to another part of the body.

• Chemotherapy is effective against cancer cells because the drugs love to interfere with rapidly dividing cells. The side effects of chemotherapy come about because cancer cells aren't the only rapidly dividing cells in your body. The cells in your blood, mouth, intestinal tract, nose, nails, vagina, and hair are also undergoing constant, rapid division. This means that the chemotherapy is going to affect them, too.

Cancer and Radiation• Cancer Cells: Body cells that are growing

without a “purpose”…their growth gets in the way of body functions.

• Radiation: Kills ALL cells, but mostly fast-growing cells…which is a cancer cell. Note: warning for x-rays and pregnancy

Applications to RadiationAlthough radiation can be harmful, there are many ways in which it can be useful in the field of medicine.

Neutron activation analysis is a procedure used to detect trace amounts of elements in samples.

Radioisotopes are used to detect cancer. For example, Iodine 131 is given to a patient in a slurry, to detect thyroid problems. The amount of iodine uptake is measured by a scan of the patient’s throat with a radiation detector.

Phosphorous-32 is used to detect skin cancer; technetium-99 detects brain tumors and liver damage.

Development of the Periodic TableDevelopment of the Periodic Table • Mendeleev (1834-1907) – He was the first to construct a

periodic table • He took the 70 elements that had been discovered by the

mid 1800’s and arranged them in columns of increasing atomic mass. Then put the elements with similar properties side by side

• Moseley (1887-1915) – He determined atomic number of atoms in elements and arranged elements by atomic number instead of atomic mass, the way Mendeleev did.

• Moseley’s way is the way that we arrange the periodic table today.

MendeleevMoseley

The Modern Periodic TableThe Modern Periodic Table • Periods- horizontal rows

• Groups- vertical columns, arranged by properties

• Periodic Law- when the elements are arranged in order of increasing atomic number, there is a periodic repetition of there physical and chemical properties.

Metals vs. Non MetalsMetals vs. Non Metals

• Lustrous-shiny• Good conductors of

Heat and

• Ductile-stretched into wire

• Malleable • + oxidation number

• Non lustrous -dull• Poor conductors of

Heat and

• Non ductile• brittle • - oxidation number

METALS NON METALS