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Atomic Structure. Anthony Gates. Atoms. The smallest particle within an element that still retains its identity in a chemical reaction. Early Ideas. Democritus: believed that the atom was indivisible and indestructible particles. His ideas were later challenged
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Atomic Structure Anthony Gates
Atoms • The smallest particle within an element that still retains its identity in a chemical reaction.
Early Ideas • Democritus: believed that the atom was indivisible and indestructible particles. • His ideas were later challenged • Dalton used experimental methods to observe the patterns to which elements combined to form new products to turn Democritus’ ideas into scientific theory.
(John) Dalton’s Atomic Theory • All elements consist of tiny indestructible particles called atoms • Atoms of the same element are identical. The atoms of any one element are different from those of any other element. • Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds. • Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.
Electrons • Discovered by J.J. Thomson • Negatively charged subatomic particles • Located in the electron cloud • Weighs 9.11 x 10-28 grams • So practically nothing • Symbol: e-
Proton • Discovered by Earnest Rutherford • Positively charged subatomic particle • Located in the nucleus • Weighs 1.67 x 10-24 grams • So practically nothing… but still more than an electron. • 1amu • Symbol: p+
Neutron • Discovered by James Chadwick • Neutral (no charge) subatomic particle • Located in the nucleus • Weighs 1.67 x 10-24 grams • So practically nothing… but still more than an electron. • 1amu • Symbol: n0
Recap • Dalton says what about the atom? • Elements made up of tiny indestructible particles • Atoms are the same as atoms of the same element and different from atoms of different elements • Atoms of different elements can mix together or combine to create compounds of atoms in whole number ratios • Chemical reactions occur when atoms interact. Atoms cannot change into an atom of a different element.
Recap part dos • Three subatomic particles are… • Electrons, protons, neutrons • Electrons are ________ charged. • Protons are ________ charged. • Neutrons are ________ charged.
Homework Answer questions from your book: • Pg. 103 • # 4, 5 • Pg. 108 • # 8, 10 • Pg. 122 • #34, 36, 37
Thomson’s Model • Believed atom was a positively charged ball containing electrons • Commonly known as the Plum Pudding model
Nucleus • Tiny central core of an atom and is composed of protons and neutrons.
Rutherford’s Model • Nucleus in the center containing protons and neutrons with a net positive charge • Electrons are evenly distributed around the nucleus taking up most of its volume.
Nucleus Size • If the nucleus was the size of a marble, then the atom would be about the size of a football stadium. • The nucleus contains a large majority of the atoms weight, but only a tiny amount of its size.
Assess for learning • Turn to a partner and describe what the Rutherford model of the atom looks like. • Include words like: • nucleus, electrons, electron cloud, protons, and neutrons.
Inquiring minds want to know… • How do we distinguish between the elements? • Elements are different because they contain different amounts of protons.
The Atomic Number (insert booming voice) • Atomic number: • The number of protons in a nucleus of an atom of an element • Ex. Hydrogen has one proton and thus its atomic number is 1. • Ex. Oxygen has eight protons and so its atomic number is 8. • This number will NEVER change for an element
Will that be cash or check? … Charge it baby! • An atom naturally has a neutral (zero) electrical charge • If the atomic number tells us the number of protons, which have a positive charge what does it also tell us about the electrons? • The atomic number is also the number of electrons • The amount of electrons must equal the number of protons to have a neutral atom.
What about neutrons??? • The atomic number will tell us how many electrons and protons there are, but how do we know how many neutrons there are?
Mass Number • Since the majority of the mass is in the nucleus as protons and neutrons, we can look at the weight to help us find the number of neutrons. • Because 1 proton or neutron weighs 1amu, the mass number will be directly related to the number of protons and neutrons. • Since helium has a atomic number of 2, it has 2 protons. If it has a mass number of 4amu, 2amu of the 4amu is the mass are because of the protons, but what about the other two? • The other 2amu is the mass of the neutrons. 2amu 2 neutrons.
#Neutron Number of Neutrons = Mass Number – Atomic Number
Chemical Symbols • Each element has its own chemical symbol. • These are one or two letter combinations • Examples • Oxygen: O • Helium: He • Gold: Au
Isotopes • Atoms that have the same number of protons, but a different number of neutrons. • Because isotopes have different numbers of neutrons, they have different mass numbers. • Isotopes retain their chemical properties since the number of protons and electrons have not changed. • p+ and e- are responsible for chemical properties
Example • Hydrogen has one proton and no neutrons, thus giving it a mass number of 1. • Hydrogen-1 • An isotope of hydrogen has one proton and one neutron, thus giving it a mass number of 2. • Hydrogen-2
Atomic Masses • Because the mass of a single element is significantly small, they are impractical to work with. • It would instead be easier to use relative masses of atoms and select a reference isotope. • Carbon-12 was selected and 1/12 of the mass of a carbon-12 atom became what is now known as 1 atomic mass unit (amu)
Atomic Masses continued... • A sample of almost any element contains a mixture of two or more isotopes. • Certain isotopes occur more often than others. • The atomic mass is a weighted average mass of the atoms in a naturally occurring sample of the element. • The weighted average reflects both the mass and the abundance of each isotope present
Calculating Atomic Mass • Carbon-12 makes up 98.89% of any sample of carbon, while carbon-13 makes up 1.11% of carbon. Atomic mass of carbon= (12.00amu x .9889) + (13.00amu x .0111) = 12.01amu
Rutherford Model of Carbon e e e 6P 6N e e e
Problems • Rutherford’s model could not explain chemical properties of elements. • Examples: • Why some compounds give off certain colors when heated in a flame. • Why do some metals glow red, then yellow and even white as they are heated to higher temperatures.
Niels Bohr • Bohr proposed that electrons are found in only in specific circular paths, or orbits, around the nucleus • Each orbit around the nucleus has a fixed energy called energy levels. • Only works well for hydrogen atoms
Ladder Analogy • The farther up the ladder, the higher the energy level • The farther up the ladder, the lower amount of energy to jump an energy level • Electrons can jump energy levels by gaining energy • Quantum: the amount of energy required to jump an energy level • You can’t stand between rungs • An electron doesn’t exist between energy levels
Bohr’s Model • In order to draw a Bohr model of an atom, simply draw the nucleus with a couple circles around it to symbolize the electron orbits. • Then draw in electrons on the orbits with only two on the most inner circle and up to eight on each of the other orbits. • Ex. Neon is shown to the right. • Practice drawing the Bohr model of carbon
Edwin Schrödinger • Devised a mathematical equation describing the behavior of an electron in a hydrogen atom. • Quantum Mechanical Model • Determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus. • This is the currently accepted model.
Location by probability • Think of a propeller blade spinning around. It is difficult to locate it at any given moment, but to locate the region where the propeller is most likely to be located at any given moment is very easy. • Electrons move even faster than propeller blades and so determining their exact location is difficult, but determining the region they are most likely to be found is much easier.
Atomic Orbitals • Atomic orbitals: region in space where there is a high probability of finding an electron.
Homework: • Pg. 132 • # 1, 2, 3, 5, 6 • Draw the Bohr model of the following elements: • Hydrogen, Beryllium, Nitrogen and Fluorine