Atomic Theory The Particle Theory of Matter

Atom – the smallest particle that has the properties of an element Atom – the smallest particle that has the properties of an element - comes from the word “Atomos” - comes from the word “Atomos” - 92 naturally occurring, 25 found in labs - 92 naturally occurring, 25 found in labs Element – A substance that can not be broken down into simpler substances Element – A substance that can not be broken down into simpler substances

Foundations of Atomic Theory Democritus Pre-Socratic Greek Philosopher Pre-Socratic Greek Philosopher Student of Leucippus Student of Leucippus Co-originator of the belief that all matter is made up of various indivisible elements which he called “Atomos” Co-originator of the belief that all matter is made up of various indivisible elements which he called “Atomos” The word Atom is derived from Atomos The word Atom is derived from Atomos His Theory His Theory 1. All matter is composed of atoms 1. All matter is composed of atoms 2. Atoms can not be divided into smaller parts 2. Atoms can not be divided into smaller parts 3. There is a void (empty space) between atoms 3. There is a void (empty space) between atoms 4. Atoms are completed solid 4. Atoms are completed solid 5. Atoms are homogeneous 5. Atoms are homogeneous 6. Atoms differ in size and shape 6. Atoms differ in size and shape His theory had no scientific proof His theory had no scientific proof

John Dalton Teacher of mathematics and chemistry Teacher of mathematics and chemistry Observer of meteorology Observer of meteorology It is from his studies of the atmosphere that lead him to devise a system of chemical symbols It is from his studies of the atmosphere that lead him to devise a system of chemical symbols 1803 – Formulated the Law of Definite and Multiple Proportions 1803 – Formulated the Law of Definite and Multiple Proportions Discovered butylene; determined composition of ether Discovered butylene; determined composition of ether 1808 – proposed his own atomic theory 1808 – proposed his own atomic theory His Theory His Theory 1. Elements are made of atoms 1. Elements are made of atoms 2. The atoms of an element are identical in their masses 2. The atoms of an element are identical in their masses 3. Atoms of different elements have different masses 3. Atoms of different elements have different masses 4. Atoms combine in small, whole number ratios 4. Atoms combine in small, whole number ratios His theory had scientific proof His theory had scientific proof

The Atom Contains a nucleus and electron cloud Contains a nucleus and electron cloud Contains 3 subatomic particles: proton, neutrons, electrons Contains 3 subatomic particles: proton, neutrons, electrons Protons and neutrons are found in the nucleus Protons and neutrons are found in the nucleus Protons and neutrons are actually made up of smaller particles called QUARKS Protons and neutrons are actually made up of smaller particles called QUARKS Electrons are found orbiting inside the electron cloud Electrons are found orbiting inside the electron cloud All un-reacted atoms have a neutral charge (that is they have a charge of 0) All un-reacted atoms have a neutral charge (that is they have a charge of 0)

Subatomic Particles ParticleCharge Mass (kg)Location Proton x in the nucleus Neutron x in the nucleus Electron x electron cloud

Fundamentals of a Neutral Atom The number of protons an atom has is called the atom’s ATOMIC NUMBER (Z) The number of protons is equal to the number of electrons The number of protons and neutrons an atom has is called the atom’s ATOMIC MASS NUMBER (A )

For Instance Carbon has an atomic number of 6 This means that it has 6 protons and 6 electrons atomic number = # protons = # electrons Carbon has an atomic mass of 12 This means that it has 6 protons and 6 neutrons atomic mass = # protons + # neutrons

Fundamentals of a Reacted Atom Atoms can gain or lose electrons. When this happens the new atom is called an ION. The energy needed to do this is called IONIZATION energy. A gain of one or more electrons results in an overall negative charge This ion is called an ANION A loss of one or more electrons results in an overall positive charge This ion is called a CATION Atoms can gain or lose neutrons. When this happens the new atom is called an ISOTOPE of the original atom. For most elements, both stable and radioactive isotopes are known. Radioactive isotopes are used as tracers in medical, biological, and industrial research

For Instance Sodium has an atomic number of 11 if it loses an electron it will only have 10 left BUT it still has 11 protons Therefore atomic number = = +1 Fluorine has an atomic number of 9 If it gains an electron it will now have 10 BUT it still has 9 protons Therefore atomic number = = - 1

Isotopes of Hydrogen Hydrogen has 3 naturally occurring isotopes Naturally Hydrogen has 1 proton and 0 neutrons PROTIUM If Hydrogen gains 1 neutron it still has 1 proton DEUTERIUM If Hydrogen gains 2 neutrons it still has 1 proton TRITIUM

Counting Atoms SI unit for the amount of a substance is the mole (mol) SI unit for the amount of a substance is the mole (mol) Counting unit Counting unit Defined as the amount of substance that contains as many elementary things (atoms, molecules, particles) as there are atoms in C-12 Defined as the amount of substance that contains as many elementary things (atoms, molecules, particles) as there are atoms in C-12 1 mole contains x particles – Avogadro's Constant 1 mole contains x particles – Avogadro's Constant ex: 1 mole H = x atoms 1 mole Ca= x atoms 1 mole Ca= x atoms 1 mole Au = x atoms 1 mole Au = x atoms Molar Mass- mass of one mole of a substance expressed as g/mol Molar Mass- mass of one mole of a substance expressed as g/mol Ex: Hg200.59g/mol Li 6.94 g/mol Li 6.94 g/mol

Gram/Mole/Atoms Conversions Ex: How many moles of atoms does gm of zinc metal contain? Ex: How many moles of atoms does gm of zinc metal contain? 1. Find the amu of Zn—65.38 amu (Atomic Mass Unit) 2. Use the equivalent mol Zn = g Zn 3. Use dimensional analysis to solve gm x 1 mol Zn atoms = 3.75 mol of Zn atoms gm Zn gm Zn

Ex: How many atoms are contained in Ex: How many atoms are contained in mol of zinc atoms? mol of zinc atoms? 1. Use the equivalent mol Zn = x atoms 2. Use dimensional analysis to solve mol Zn x x atoms = 7.53 x Zn atoms 1 mol Zn

Ex: Calculate the mass of one aluminum atom in grams. Ex: Calculate the mass of one aluminum atom in grams. 1. Use the equivalents mol Al = g Al 1 mol Al = g Al 1 mol Al = x Al atoms 1 mol Al = x Al atoms 2. Use dimensional analysis to solve g Al x 1 mol of Al_____ 1 mol Al 6022 x Al Atoms = X g Al/Al atom Therefore--- mass of 1 Al atom = x g

Models of the Atom Niels Bohr Suggested that electrons orbit the nucleus like the planets around the sun The path electrons travel defines it energy level Electrons can only travel in certain energy levels To move to another energy level the electron must gain or lose energy must gain or lose energy Electrons found in the outer most energy level are called VALENCE ELECTRONS

Wave Model – 1925 Uses the same principles as Bohr Model but instead of definite paths suggests the possible path probability of an electron This is the notion of the electron cloud Electrons are found in regions called ORBITALS Each orbital can hold a maximum of 2 electrons

There are seven energy levels (1-7) and 5 orbitals The most common are listed below The 5 th orbital -g-exists for the principal quantum number 5 and higher OrbitalMaximum number of electrons s 2 s 2 p 6 p 6 d 10 d 10 f14 f14 ** We will learn more about this with our study of the periodic table