Atomic Structure

Early Theories of Matter Democritus ( BCE) Democritus ( BCE) Greek philosopher Greek philosopher First to propose the concept of the atom First to propose the concept of the atom The word atom comes for Greek atomos which means indivisible The word atom comes for Greek atomos which means indivisible Had no experimental data to support his theories Had no experimental data to support his theories Aristotle disagreed with the theory of atoms so the whole idea was rejected Aristotle disagreed with the theory of atoms so the whole idea was rejected

John Dalton ( ) English school teacher English school teacher Developed the basis for the Modern Atomic Theory Developed the basis for the Modern Atomic Theory Developed ideas based on scientific experiments Developed ideas based on scientific experiments Dalton’s work was a huge step toward the understanding of the atom but not completely accurate. Can you tell which parts are not true? Dalton’s work was a huge step toward the understanding of the atom but not completely accurate. Can you tell which parts are not true?

Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. All matter is composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties. All atoms of a given element are identical, having the same size, mass and chemical properties. Atoms cannot be created, divided or destroyed. Atoms cannot be created, divided or destroyed. Different atoms combine in simple whole- numbered ratios to form compounds. Different atoms combine in simple whole- numbered ratios to form compounds. In a chemical reaction, atoms are separated, combined or rearranged. In a chemical reaction, atoms are separated, combined or rearranged.

People to Know… William Crookes – discovered the cathode ray which led to the eventual development of the television William Crookes – discovered the cathode ray which led to the eventual development of the television J.J. Thomson later used the cathode ray tube to discover the 1 st subatomic particle -the electron – and that electrons from different elements were alike. J.J. Thomson later used the cathode ray tube to discover the 1 st subatomic particle -the electron – and that electrons from different elements were alike. This was the first proof that atoms were made of smaller parts. This was the first proof that atoms were made of smaller parts. Thompson suggested the “plum pudding” model of the atom. Thompson suggested the “plum pudding” model of the atom.

More People… Ernest Rutherford – Conducted experiments firing radiation at a piece of gold foil. He expected all of the radiation to pass through and was very surprised when some of the particles were deflected. This led to the discovery of the NUCLEUS and the theory of the nuclear atom. Ernest Rutherford – Conducted experiments firing radiation at a piece of gold foil. He expected all of the radiation to pass through and was very surprised when some of the particles were deflected. This led to the discovery of the NUCLEUS and the theory of the nuclear atom. entialchemistry/flash/ruther14.swf entialchemistry/flash/ruther14.swf entialchemistry/flash/ruther14.swf entialchemistry/flash/ruther14.swf

Still More… 8 years later (1920), Rutherford discovered the proton – a subatomic particle located in the nucleus with a charge equal, but opposite of the electron. 8 years later (1920), Rutherford discovered the proton – a subatomic particle located in the nucleus with a charge equal, but opposite of the electron. 12 years later (1932), James Chadwick discovered the neutron – a particle in the nucleus with a mass nearly equal to the proton but with no electrical charge. 12 years later (1932), James Chadwick discovered the neutron – a particle in the nucleus with a mass nearly equal to the proton but with no electrical charge.

Homework Create a time line with the scientists from your notes and include their name and major contribution to current atomic theory. (see pages in your book) Create a time line with the scientists from your notes and include their name and major contribution to current atomic theory. (see pages in your book) Add three additional scientists that have made new contributions to our understanding of the atom since the discovery of the neutron and be prepared to share what they discovered. Add three additional scientists that have made new contributions to our understanding of the atom since the discovery of the neutron and be prepared to share what they discovered.

Subatomic Particles proton neutron electron proton neutron electron + = - + = - nucleus nucleus electron nucleus nucleus electron cloud cloud 1.673x g 9.1x g 1.673x g 9.1x g 1.675x g 1.675x g 1 amu 1 amu 0 amu 1 amu 1 amu 0 amu Relative Charge Location Actual Mass Mass Number

What is an AMU ??? amu (atomic mass unit): a unit used to express very small masses a unit used to express very small masses based on the mass of one carbon-12 atom based on the mass of one carbon-12 atom 1 amu = x g 1 amu = x g

So, how small is an atom? World population World population Atoms in a penny Atoms in a penny

Atomic Nucleus ~ m nucleus tiny, positively charged, center of atom tiny, positively charged, center of atom contains protons and neutrons contains protons and neutrons contains most of the mass of an atom contains most of the mass of an atom ~ m

Atoms If all atoms are composed of protons, neutrons, and electrons, then why do different types of atoms have different properties? If all atoms are composed of protons, neutrons, and electrons, then why do different types of atoms have different properties? The differences between atoms of different elements is due entirely to the differences in the numbers of p, n, and e - in each type of atom.

Atoms Atomic number: the number of protons in the nucleus Atomic number: the number of protons in the nucleus Example: Example: Carbon: 6 p (atomic # = 6) Carbon: 6 p (atomic # = 6) Sulfur: 16 p (atomic # = 16) Sulfur: 16 p (atomic # = 16)

Atoms Each atom contains the same number of electrons as protons. Each atom contains the same number of electrons as protons. (that’s why atoms are electrically neutral) Helium: Helium: Magnesium: Magnesium: Iron: Iron: 2 p, 2 e- 12 p, 12 e- 26 p, 26 e-

Atoms Atomic mass: the number of protons + the number of neutrons Atomic mass: the number of protons + the number of neutrons Example: Example: Carbon-12 = __ p + + __n Carbon-12 = __ p + + __n Mercury-201 = ___ p + + ___ n Mercury-201 = ___ p + + ___ n

Nuclear Symbols - represents a specific atom MassNumberAtomicNumber X

Isotopes Atoms that have the same atomic number but different mass numbers (different numbers of neutrons) Examples Examples Carbon-12 (6 p, 6 n) Carbon-12 (6 p, 6 n) Carbon-14 (6 p, 8 n) Carbon-14 (6 p, 8 n)

Isotopes Most elements have at least two isotopes. Most elements have at least two isotopes. The naturally occurring isotopes of each element are present in specific ratios. The naturally occurring isotopes of each element are present in specific ratios. Oxygen % Oxygen % Oxygen % Oxygen % Oxygen % Oxygen %

Average Atomic Mass Weighted average of the atomic masses of the naturally occurring isotopes of an element. Weighted average of the atomic masses of the naturally occurring isotopes of an element. Multiply the mass of each isotope by its percentage abundance then add all of the parts! Multiply the mass of each isotope by its percentage abundance then add all of the parts! (why is division not required?) (why is division not required?)

Example – Two isotopes of copper occur in nature % of copper atoms have a mass of 62.94u and 30.83% have a mass of 64.93u. What is the average atomic mass?

Naturally occurring chlorine is 75.53% chlorine-35 which has a mass of amu and 24.47% chlorine-37 which has an atomic mass of amu. Calculate the average atomic mass of chlorine.

An element consists of three naturally occurring isotopes with masses , , and amu. The relative abundances of these three isotopes are 78.70, and percent respectively. Calculate the average atomic mass. What is the element?