2 Atomic Structure – timeline Ancient Greece - Democritus proposed the atom – a tiny solid particle that could not be subdivided.1904 – J.J. Thomson – discovered that atoms contained small, negatively charged particles called electrons.
3 Dalton’s Atomic Theory (#9) Every element is made of tiny, unique, particles called atoms that cannot be subdivided.Atoms of the same element are exactly alike.Atoms of different elements can join to form molecules or compounds
4 1911 – Ernest Rutherford – proposed that the atom had two parts – the nucleus in the center (most of the mass) surrounded by the electrons.1913 – Niels Bohr –hypothesized thatelectrons traveled in fixedorbits around the atom’s nucleus.
5 1913 – James Chadwick – concluded that the nucleus contained positive protons and neutral neutrons. 1926 – Erwin Schrodinger – developed the quantum mechanical model – which is based on the wavelike properties of the electron. (not a particle – leads to quantum physics)
6 1927 – Werner Heisenberg – (the Heisenberg uncertainty Principle) described that it is impossible to know precisely both an electron’s position and path at a given time. Led to the electron cloud theory.
7 AtomsThe smallest particle that has the properties of an element.
8 Parts of an AtomNucleus – small, dense center of an atom made up of 2 subatomic particles that are identical in size and mass.Protons – have apositive chargeNeutrons – have no charge
9 Parts of an Atom cont.Electrons – are tiny subatomic particles that have very little mass that moves around the outside of the nucleus. These particles are negatively charged and form a“cloud” aroundthe nucleus.
10 The number of protons and electrons an atom has is unique for each element.
11 Atomic ChargeAtoms have no overall charge because the protons (+) cancel out the electrons (-).Helium protons2 neutrons2 electronstotal charge 0
12 Protons positive (+) charge Found in the nucleus # of protons = atomic #The number of protons identify the element (atomic #)
13 Neutrons no charge Found in the nucleus Along with protons makes up atomic massAtomic Mass – atomic number = # of neutrons(rounded to whole #)
14 Electrons negative (–) charge travel in orbitals (or energy levels) around the nucleus. (electron cloud)Equals atomic number in neutral atomsvalence electrons - the # of electrons in the outer shell and relates to the oxidation #
15 Unit of measure for atomic particles is Atomic mass unit (amu) protons and neutrons = about 1 amu (electrons are about 1/2000 of the size of protons and neutrons))
16 Chemical symbolsThe one or two letter abbreviation of the element name.Some are based on Latin nameALL 1st letter is upper caseALL 2nd letter is lower case
17 Mass Number or Atomic Mass the sum of the number of protons and the number of neutrons in the nucleus of an atom.# of neutrons =mass # - atomic #NeutronsProtons+
18 Atom Summary Atomic Number = protons = electrons Atomic Mass = Protons + NeutronsNeutrons = atomic mass – atomic numberAtomic symbolsFirst letter is ALWAYS upper caseSecond letter is ALWAYS lower caseExample: Identify the Number of Protons, Neutrons and Electrons in OxygenOxygen element 6 with mass 16P = 8 N = 16-8 = 8E = 8
19 Atom SummaryExample 2: Identify the Number of Protons, Neutrons and Electrons in Sulfur and Sodium
20 IsotopesAtoms of the same element that have a different # of neutrons and a different atomic mass. (identified by the element name followed by the mass # )ex. C-12, C-14, B-10, B-11)Carbon 14 = 8 neutrons6 protons6 electrons6 electrons6 protonsCarbon 12 = 6 neutrons
21 Average atomic massthe weighted - average mass of the mixture of all an atoms isotopes. The average atomic mass is close to the mass of its most abundant isotope.This is the number found on the periodic table
22 Using Bohr’s Atomic Model Bohr was the 1st person to propose the concept of electrons having specific energy levelsThis explained how electrons could give off light ( by gain or lose energy)Bohr’s Model can be used to show how the electrons will arrange themselves around a nucleus.
23 BOHR MODELElectrons are placed in energy levels surrounding the nucleusYou fill the lower energy levels first1st energy level can hold max of 2 electrons2nd energy level can hold max of 8 electrons3rd energy level can hold max of 18 electrons4th energy level can hold max of 3218e-8e-Nucleus(p+ & n0)2e-
24 ExampleChlorine 17 protons 17 electrons 18 neutrons Valance Electrons: Electrons found in outer energy level. Chlorine has 7 electrons in outer energy level (ring 3)