History of the Atom Scientists and Their Discoveries
Democritus(460 BC – 370 BC) Proposed an Atomic Theory which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes. Aristotle did not support his atomic theory Image taken from: https://reich-chemistry.wikispaces.com/T.+Glenn+Time+Line+Project
Antoine Lavoisier(1743 – 1794) Known as the “Father of Modern Chemistry” Was the first person to generate a list of thirty-three elements in his textbook Devised the metric system Married to a 13-year old Marie-Anne Pierette Paulze; she assisted him with much of his work Was guillotined during the French Revolution Discovered/proposed the Law of Conservation of Mass Image taken from: www.ldeo.columbia.edu/.../v1001/geotime2.html
John Dalton (1766 – 1844) In 1803, proposed an Atomic Theory which states: All substances are made of atoms; atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, and atoms of different elements are different Atoms join with other atoms to make new substances Calculated the atomic weights of many various elements Image taken from: chemistry.about.com/.../John-Dalton.htm
J.J. Thomson (1856 – 1940) Proved that an atom can be divided into smaller parts Discovered electrons Stated that the atom is neutral In 1897, proposed the Plum Pudding Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material Won a Nobel Prize Image taken from: www.wired.com/.../news/2008/04/dayintech_0430
Ernest Rutherford (1871 – 1937) In 1909, suggested the following characteristics of the atom: Has a nucleus that contains most of the mass of the atom and is made up of particles called protons, which have a positive charge The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space Did extensive work on radioactivity and was referred to as the “Father of Nuclear Physics” Won a Nobel Prize Was a student of J.J. Thomson Image taken from: http://www.scientific-web.com/en/Physics/Biographies/ErnestRutherford.html
Niels Bohr (1885 – 1962) In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy) Won a Nobel Prize Worked with Ernest Rutherford Image taken from: commons.wikimedia.org/wiki/File:Niels_Bohr.jpg
Erwin Schrodinger (1887-1961) In 1926, he further explained the nature of electrons in an atom: The exact location of an electron cannot be stated It is more accurate to view the electrons in regions called electron clouds; electron clouds are places where the electrons are likely to be found Won a Nobel Prize Image taken from: nobelprize.org/.../1933/schrodinger-bio.html
James Chadwick (1891 – 1974) Realized that the atomic mass of most elements was double the number of protons discovery of the neutron in 1932 Worked on the Manhattan Project Worked with Ernest Rutherford Won a Nobel Prize Image taken from: www.wired.com/.../news/2009/02/dayintech_0227
+ + + The Building Blocks of Matter: Atoms - - - + + + - - + + - - -
Matter • Anything that has mass and takes up space (volume) • Examples: • A brick has mass and takes up space • A desk has mass and takes up space • A pencil has mass and takes up space • Air has mass and takes up space All of the above examples are considered matter because they have mass and take up space. Can you think of anything that would not be considered matter?
Atoms • Atoms- smallest possible unit into which matter can be divided, while still maintaining its properties. • Made up of: • protons • neutrons • electrons • The solar system is commonly used as an analogy to describe the structure of an atom - + For example, what is the smallest possible unit into which a long essay can be divided and still have some meaning? - + + - + + - -
www.deckersfoods.com Atoms are so small that… • A stack of 50,000 aluminum atoms = the thickness of a sheet of aluminum foil from your kitchen. • If you could enlarge a penny until it was as wide as the US, each of its atoms would be only about 3 cm in diameter – about the size of a ping-pong ball • Human hair is about 1 million carbon atoms wide. • Typical human cell contains roughly 1 trillion atoms. • A speck of dust might contain 3x1012 (3 trillion) atoms. • It would take you around 500 years to count the number of atoms in a grain of salt. C-C-C-C-C-… + 999,995 more 1 trillion atoms . Is made of approximately 3 trillion atoms Just one of these grains
Let’s Experiment In order to try to gain an idea of how small an atom really is, you will complete the following activity. • Cut a strip of 11 in. paper in half. • Discard one half. • Cut the remaining piece in half. • Continue cutting the pieces in half and discarding the strips as many times as you can, counting the number of cuts you make
Results • How many cuts were you able to make? • Do you think you could keep cutting the paper forever? Why or why not? You would have to cut the paper in half around 31 times to get to the size of any atom. http://www.miamisci.org/af/sln/phantom/papercutting.html
- - - + + + + - - + + - + + - - Protons (+) • Protons- positively charged particles • Make up part of the nucleus of the atom • Identify the atom • Equal to the atomic number of the atom • Contribute to the atomic mass • Equal to the number of electrons +
- - - + + + + - - + + - + + - - Neutrons • Neutrons- neutral particles; have no electric charge • Help make up the nucleus of the atom • Contribute to the atomic mass
- - - + + + + - - + + - + + - - Electrons (-) • Electrons- negatively charged particles • Found outside the nucleus of the atom in electron orbits/levels • Each orbit/level can hold a maximum number of electrons 1st = 2, 2nd = 8, 3rd = 8 • When the orbitals are full, the atoms are stable! • This Octet Rule for atoms with < 20 electrons is 2, 8, 8, 8 • > 20 disregard -
Electrons (-) • Move so rapidly they create an electron cloud • Mass is insignificant • Equal to the number of protons • Valence electrons- the outermost electrons involved in the formation of chemical bonds
+ + + The Atom’s “Center” • Protons and neutrons are grouped together to form the “center” or nucleus of an atom. Notice that the electrons are not apart of the nucleus - - -
QUARKS • Particles that make up protons and neutrons Notice the smaller particles that make up this neutron after you take a closer look. Notice the smaller particles that make up this proton after you take a closer look. + What do you notice about the number of quarks in the neutron and proton?
- - - - - - - - - - - - - - - - - - + + - - - - - - - - - - - - - - - - - - Sub-Atomic Particles Weight Comparison (protons, neutrons, electrons) Neutron = 1.6749286 x10-27 kgProton = 1.6726231 x10-27 kgElectron = 9.1093897 x10-31 kg 1839 electrons = 1 neutron 1836 electrons = 1 proton How do you think the mass of a neutron compares to that of a proton? 1 neutron ≈ 1 proton
+ + + Sub-atomic ParticlesSize Comparison (protons, neutrons, electrons, & quarks) - - - + + + - - + + - - -
Something to Think About • You’ll never see life the same way again
Elements • Element- made up of one kind of atom that can’t be broken down into simpler substances by physical or chemical means • 90 occur naturally on Earth • 25 were synthesized (made) by scientists
The Periodic Table Elements • Boxes in the periodic table contain a lot of information. To understand this information, it is necessary to refer to the periodic table’s key Atomic Number Element Symbol (a capital letter or a capital followed by a lower case letter) Element Name Atomic Mass
+ + + Atomic Number • Atomic number- the number of protons in the nucleus of an atom • Equal to the number of electrons to make an atom neutral - What would be the atomic number of this atom? - -
+ + + Atomic Mass • Atomic mass- the total number of protons and neutrons in an atom’s nucleus • Expressed in Atomic Mass Units (amu) • Each proton or neutron has a mass of 1 amu What would be the atomic mass of this atom? - + 3 4 - 3 protons + 4 neutrons = an atomic mass of 7 amu Why did we not account for the electrons when calculating the atomic mass? -
+ = 8 = 8 = 8 + + + - How to Obtain the Number of Sub-Atomic Particles in an atom using a Periodic Table - - - 8 + + + O - - + + Oxygen - 15.9994 - - Protons Neutrons Electrons + - Equal to the atomic mass (rounded to a whole #) minus the # of protons Equal to the atomic # on the Periodic Table Equal to the # of protons Example: Determine the # of protons, neutrons, and electrons in an atom of oxygen. Protons = 8 (Atomic #) Neutrons = 8 (Rounded atomic mass minus atomic #) Electrons = 8 (# of P) Neutron Calculations = 16 (P + N) – 8 (P) = 8 N
= 1 = 0 = 1 + - Hydrogen (H) Atom • Bohr electron diagrams- show ALL the electrons in an atom. Notice the 1 electron in the 1st orbital • The rule is 2 in the first orbital, then 8, 8 = full and stable (unreactive) - How many more electrons can fit in the 1st orbital/ level? + Even though there are no neutrons present, Hydrogen is still considered an atom
+ = 8 = 8 = 8 + + + - Oxygen (O) Atom • Notice the two electrons in the first orbital/level and the six in the second How many more electrons can fit in the 2nd orbital/ level? - - - + + + - - + + - - -
+ = 11 = 12 = 11 + + + - Sodium (Na) Atom • Notice the two electrons in the first orbital/level, eight in the second, and one in the third - - - How many more electrons can fit in the 3rd orbital/ level? - + + + - - - + + - - - -
Lewis Structure(Electron Dot Diagram) • Valence electrons- the electrons in the outermost shell that are responsible for how an atom will behave chemically • Lewis Dot Structure- way of drawing ONLY the valence electrons of an atom • Element symbol surrounded by as many dots as there are valence electrons • Examples How many valence electrons do each of these atoms have?
Counting Valence Electrons Carbon 4 valence electrons Beryllium 2 valence electrons Oxygen 6 valence electrons
Check for Understanding How Many Valence Electrons? • Hydrogen • Potassium • Neon • Sulfur • Calcium 1 Valence Electron 1 Valence Electron 8 Valence Electrons 6 Valence Electrons 2 Valence Electrons
Making an Electron Dot Diagram Element “X” has 8 valence electrons Write down the element’s symbol and place the first two dots on any side of the symbol. If this were an atom of an element from group 1, you would just place the one dot on any side of the element. Place the rest of the dots in either a clockwise or counter clockwise manner around the symbol, with no side receiving two dots until each side gets one.
Check for Understanding 1 Valence Electron 6 Valence Electrons H O How many valence electrons does each atom have? Ne Mg 2 Valence Electrons 8 Valence Electrons
+ = 8 = 8 = 8 + + + - Ion • Charged particle that typically results from a loss or gain of electrons • Two types: • Anion = negatively charged particle • Cation = positively charged particle - - - + + + - - 6 9 + + - - Now that three electrons were lost, the number of electrons (6) and protons (8) is still unbalanced; therefore, it is still an ion, but now it is specifically referred to as a cation. Now that this atom of oxygen just gained an electron, it is no longer neutral or an atom. It is now considered an ion (anion). This ion has more electrons (9) than protons (8). Currently, this atom of oxygen is neutral because it has an equal number of electrons (8) and protons (8). - - Symbol = O2+ Symbol = O1- Symbol = O
Building Ions Be aware that the atomic and atomic mass are not impacted by the loss or gain of electrons.
Isotopes • Isotopes- atoms that have the same number of protons, but have different numbers of neutrons • Examples Notice that each of these atoms have one proton; therefore they are all types of hydrogen. They just have a different atomic mass - - + + + - Hydrogen (Protium) Hydrogen (Deuterium) Hydrogen (Tritium)
Isotopes • Recall that the atomic mass is the number of neutrons and protons in an atom • Example - + + + - - Hydrogen (Protium) Atomic mass # = 1 amu Hydrogen (Deuterium) Atomic mass # = 2 amu Hydrogen (Tritium) Atomic mass # = 3 amu
FORCES IN THE ATOM • Gravitational Force • Electromagnetic Force • Strong Force • Weak Force
Gravitational Force • The force of attraction of objects due to their masses • The amount of gravity between objects depends on their masses and the distance between them Do you think this force plays a significant role in holding the atom together?
Electromagnetic Force • The force that results from the repulsion of like charges and the attraction of opposites • The force that holds the electrons around the nucleus + + + - - - Notice how the particles with the same charge move apart and the particles with different charges move together. Why are neutrons not pictured above?
Strong Force Notice how the electromagnetic force causes the protons to repel each other but, the strong force holds them together. • The force that holds the atomic nucleus together • The force that counteracts the electromagnetic force • This force is only strong if the protons and neutrons are close together + + + + Would an atom have a nucleus if the strong force did not exist?
Weak Force • Plays a key role in the possible change of sub-atomic particles. • For example, a neutron can change into a proton(+) and an electron(-) • The force responsible for radioactive decay. • Radioactive decay- process in which the nucleus of a radioactive (unstable) atom releases nuclear radiation. Notice how the original particle changes to something new. + n - If you need help remembering weak force, just think of…
Atoms Forces and Elements • Forces video
Periodic Table • Something “periodic” occurs at regular or generally predictable intervals • Periodic law - physical and chemical properties of the elements are periodic functions of their atomic numbers • Periodic Table of Elements – a table of the elements, arranged by atomic number, that shows the patterns in their properties; based on the periodic law Can you think of anything that is periodic?