Atomic Structure Theories and Periodic Table Structure Of

Atomic Structure, Theories and Periodic Table

Structure Of An Atom

Parts Found in Nucleus Protons Neutrons Found in shells or orbits Electrons

Protons Found in the nucleus Positively charged Determines the identity of the element. Mass = 1 amu

Neutrons Found in nucleus Neutral charge Mass = 1 amu

Electrons Found in the shells/orbits around the nucleus Negatively charged Determines chemical behavior Mass = 1/1832 amu (negligible mass)

Neutral Atoms Number of protons = Number of electrons # of Positive charges = # of Negative charges Example: A neutral atom of Neon has 10 protons and 10 electrons. A neutral atom of chlorine has 17 protons and _____ electrons.

Atomic Number Atomic number = number of protons Found on the periodic table Protons determine the identity of the element Example: If boron has an atomic number of 3 then it has 3 protons. a. If argon has an atomic number of 18, then it has ___ protons? b. What element has an atomic number of 20?

Mass Number Mass number = number of protons + number of neutrons # Neutrons = Mass # - Atomic # No mass numbers found on the periodic table Example: If an atom has 3 protons and 4 neutrons it has a mass number of 7. If an atom has a mass number of 11 and has 5 protons, it has ___ neutrons. If an atom has a mass number of 15 and an atomic number of 7, how many protons does it have? ____ How many neutrons does it have? ____

Give the number of protons and neutrons for the following atoms. Symbol Protons Electrons Neutrons

IONS Number of protons ≠ Number of electrons Positive Ion # of Positive charges > # of Negative charges 4 protons and 2 electrons Negative Ion # of Positive charges < # of Negative charges 9 protons and 10 electrons

Development of Atomic Models

Philosophies and Discoverers of the Parts (Subatomic Particles) of the Atom: Electron- Crookes, JJ Thomson, Millikan Proton- Rutherford Neutron- Chadwick

The Atom The discovery of the atom is a progression Many scientists contributed to the development of present day atomic theory. With each new discovery dealing with the nature of the atom, a new atomic model was constructed. The first person to believe in the existence of the atom was Democritus in 400 B. C.

Democritus 400 BC Democritus-suggested the existence of atoms without the support of experimental evidence.

Philosopher 2: Aristotle very influential disagreed with Democritus helped disprove Democritus’ theory of atom this caused the denial of the existence of atoms for the next 2000 years

John Dalton 1785 -1844 English school teacher that performed experiments to correct his atomic theory Believed all atoms are indivisible spheres

Dalton’s Atomic Theory John Dalton- proposed the first Atomic Theory a. All elements are composed of indivisible particles called atoms. b. Atoms of the same element are identical c. Atoms of different elements can mix physically or combine chemically in whole number ratios to form compounds d. Chemical reactions occur when atoms are separated, combined or rearranged however, atoms are never changed into another atom because of a chemical reaction.

Eugene Goldstein In 1886 used a modified cathode ray to discover canal rays and protons

John Thompson Discovered the electron in 1897 Passed electric current through gases at low pressure with as cathode ray tube Developed the Plum Pudding Model of an atom

Millikan 1909 performed Oil Drop Experiment Determined the charge to mass ratio of an electron and then determined the mass of an electron

Ernest Rutherford 1909 Performed the gold foil experiment and concluded that an atom is mainly empty space with a tiny densely-packed positive nucleus

The Proton-- Rutherford Using a gold foil experiment, he aimed a beam of radiation through a piece of gold foil, he expected the beam to go straight through. Instead, some of the radiation bounced off. Developed the nuclear atom model Discovered the existence of the nucleus Discovered the proton in the nucleus.

Neils Bohr 1913 Developed the Planetary Model of an atom with electrons orbiting the nucleus in specific orbits

Erwin Schrödinger (1926) Quantum mechanics electrons can only exist in specified energy states Electron cloud model orbital: region around the nucleus where eare likely to be found

James Chadwick (1932) Discovered neutrons neutral particles in the nucleus of an atom Joliot-Curie Experiments based his theory on their experimental evidence

The Periodic Table There are 116 elements on the periodic table. How many different types of atoms are there? 116 How do all of these atoms/elements differ from one another? They differ in the # p+, # n°, # e – The periodic table is organized left to right, top to bottom by increasing atomic number. Horizontal rows– periods Columns– families/groups

The atoms of each element contain a unique positive charge Atoms are neutral (0 charge) because they are balanced by a + and – charge. # e-- = # p+ = atomic number How many p+ and e-- are in each of the following? a. B b. Ra c. Pt d. Mg e. An atom contains 66 e--. What is it? f. An element contains 14 p+. What is it?

Atomic Mass Number and Isotopes Atomic Mass number Is the average of all masses of isotopes combined Is equal to #p+ + #n° in the nucleus To find the number of n° : = atomic mass # - atomic # = atomic mass # - #p+ = atomic mass # - #e-

Isotopes are atoms with the same number of p+, but different #n°. The number in the isotope name gives the atomic mass of the isotope. Potassium-39 and potassium-40 are isotopes. Isotopes all have basically the same chemical behavior. Why? Chemical behavior depends upon e-. Isotopes all have the same # of e-.

Ex. potassium- 39 Has an atomic mass of 39. What is the #p+ and #n° in the nucleus? #p+ = 19, #n°= 20 Ex. potassium-40 Has an atomic mass of 40. What is the #p+ and #n° in the nucleus? #p+ = 19, #n°= 21

Isotopes (find p+, e-, n 0) Element Neon Atomic Number 10 Atomic Mass Number 22 Calcium 20 46 Oxygen 8 17 Iron 26 57 Zinc 30 64 Mercury 80 204

Ex. 1 Using % Abundance to Find Atomic Mass Contribution ISOTOPE Isotope 6 X Isotope 7 X 6 X: MASS %Abund. 6. 015 amu 7. 016 amu 7. 5% 92. 5% mass contribution= (mass) (% abundance) = (6. 015 amu)(. 075) 6 X= 7 X: . 451 amu mass contribution= (mass) (% abundance) = (7. 016 amu)(. 925) = 6. 490 amu Now add the numbers together: =. 451 amu + 6. 490 amu = 6. 941 amu Element is Lithium.

Boron has 2 naturally occurring isotopes: boron-10 (abundance=19. 8%, mass=10. 013 amu), boron 11(abund. = 80. 2%, mass=11. 009 amu). Calculate the atomic mass of boron. Calculate the atomic mass of Mg. The 3 Mg isotopes have atomic masses and abund. of 23. 985 amu (78. 99%), 24. 986 amu (10. 00%), and 25. 982 amu (11. 01%).

Radioactive Decay Why don’t atoms of one element change into atoms of another element during chemical reactions? Because chemical reactions involve an atoms e-. The nucleus remains unchanged. What determines the identity of an atom? The number of protons in an atom.

Nuclear Reactions There is another type of reaction that involves the nucleus undergoing change; this reaction involves one radioactive element changing into another element- nuclear reactions. Radioactive atoms undergo significant changes that can alter their identities.

There are three types of radioactive decay: Alpha radiation (α)- made up of 2 p+ and 2 n 0; is equivalent to a He nucleus 4 He 2 Beta radiation (β)- made up of fast moving electrons called beta particles. 0 β -1 Gamma radiation (γ)- made up of high energy radiation that possess no mass or electrical charge. 0 γ 0

C. Isotopes Atoms of the same element with different numbers of neutrons. ¨ Isotope symbol: Mass # Atomic # “Carbon-12”

C. Isotopes © Addison-Wesley Publishing Company, Inc.

C. Isotopes Average Atomic Mass reported on Periodic Table weighted average of all isotopes Avg. Atomic Mass

C. Isotopes EX: About 8 out of 10 chlorine atoms are chlorine-35. Two out of 10 are chlorine 37. Avg. Atomic Mass 35. 4 u

Periodic Table atomic number # of protons mass number -atomic number # of neutrons 8 O 15. 999 round to 16 - mass number ( # protons & neutrons) unrounded –mass number (average mass of the isotopes)

Masses of Atoms l A scale designed for atoms gives their small atomic masses in atomic mass units (amu) l An atom of 12 C was assigned an exact mass of 12. 00 amu l Relative masses of all other atoms was determined by comparing each to the mass of 12 C l An atom twice as heavy has a mass of 24. 00 amu. An atom half as heavy is 6. 00 amu.

Atomic Mass l Listed on the periodic table l Gives the mass of “average” atom of each element compared to 12 C l Average atom based on all the isotopes and their abundance %. l Atomic mass is not a whole number due to isotopes. Na 22. 99

Isotopes – atoms of the same element with different numbers of neutrons. Oxygen-16 Oxygen-17 16 Oxygen-18 17 8 p+ ‗‗‗‗ e- ‗‗‗‗ nº ‗‗‗‗ 18 8 8 ‗‗‗‗ ‗‗‗‗

Calculating Average Atomic Mass l Percent(%) abundance of isotopes l Mass of each isotope of that element l Weighted average = mass isotope 1(%) + mass isotope 2(%) + … 100

Atomic Mass of Magnesium Isotopes Mass of Isotope 24 Mg = 24. 0 amu 25 Mg 26 Mg = 25. 0 amu = 26. 0 amu Abundance 78. 70% 10. 13% 11. 17% Atomic mass (average mass) Mg = 24. 3 amu Mg 24. 3

Finding An Isotopic Mass Naturally occurring boron is 80. 20% boron 11 (atomic mass 11. 0 amu) and 19. 80% of a different isotope of boron. What must the mass of this isotope be if the average atomic mass of boron is 10. 81 amu?

Radioactivity Mosely’s X-ray analysis of atoms was an attempt to explain radioactivity. 1896 – Henri Becquerel – Uranium spontaneously emits energy. 1898 – Marie & Pierre Curie – first isolated a radioactive element - Radium

The Periodic Table

A. Dmitri Mendeleev (1869, Russian) • Organized elements by increasing atomic mass. • Predicted the existence of undiscovered elements.

B. Henry Mosely (1913, British) • Organized elements by increasing atomic number. • Fixed problems in Mendeleev’s arrangement.

A. Metallic Character Metals Nonmetals Metalloids

B. Table Sections Representative Elements Transition Metals Inner Transition Metals

B. Table Sections Overall Configuration Lanthanides - part of period 6 Actinides - part of period 7

C. Columns & Rows Group (Family) Period

A. Terms Periodic Law • Properties of elements repeat periodically when the elements are arranged by increasing atomic number.

A. Terms Valence Electrons e- in the outermost energy level Atomic Radius ¨First Ionization Energy • energy required to remove an efrom a neutral atom

B. Periodic Trends Atomic Radius • Increases to the LEFT and DOWN.

B. Periodic Trends First Ionization Energy • Increases to the RIGHT and UP.

B. Periodic Trends Which atom has the larger radius? • Be or Ba Ba • Ca or Br Ca

B. Periodic Trends Which atom has the higher 1 st I. E. ? • N or Bi N • Ba or Ne Ne

B. Periodic Trends Group # = # of valence e- (except He) Families have similar reactivity. Period # = # of energy levels 1 A 8 A 2 A 3 A 4 A 5 A 6 A 7 A

C. Dot Diagrams Dots represent the valence e-. EX: Sodium ¨EX: Chlorine