Atomic Structure, The Periodic Table & Atomic Theory What’s it all about?

The Basic Atom Smallest particle of an element that still has the element’s properties Atomic Theory explains what atoms look like, and how and why they behave the way they do Democritus (400 BC) proposed the existence of atoms (philosophy) John Dalton (1800) was the first to have scientific evidence to support this Considered the Father of Modern Atomic Theory

Dalton’s Atomic Theory Dalton’s experiments showed him several things about the existence of atoms – he had 5 postulates All matter is made of atoms Atoms are small, indestructible spheres Atoms of the same element are identical Atoms always combine in compounds in whole number ratios In chemical reactions atoms are combined, separated or rearranged

Dalton’s Model The Marble Model Dalton’s idea of the atom was a small sphere hence

Current model “building blocks of matter” Charge: Neutral (no charge) particles made up of 3 subatomic particles in 2 regions Nucleus Tiny Positively charged Dense mass in the atom’s center has 2 particles (p+) protons each has a (+1) charge has a mass of 1 a.m.u.* (n) Neutrons no charge *a.m.u. = atomic mass unit Electron Cloud: Diffuse (spread out very thinly) Negatively charged area outside of the nucleus Electrons (e-): each has a (-1) charge little mass (0 amu) located outside of the nucleus

Region & Particle Relationship Atoms Nucleus Electron Cloud Region Subatomic Particle Neutron Proton electron + - Charge Charge Balance

Atomic Particles The Electron

The Electron– Fun Facts Abbreviated e- Gives the electron cloud its charge Gives the element its chemical properties Structure: Lepton (fundamental particle not made of smaller particles) Mass = 0 amu* (amu = atomic mass unit) Not really 0 but 1/1200-1/2000th the mass of a proton) Charge: negative (exactly balances the p+ positive charge) Location: Electron Cloud

The Electron on the Periodic Table How many electrons are there in an element?? Where do you find it??? 20 Ca Calcium 40.078 # of e- = Atomic Number but only in a neutral atom Let’s make a note on our PT & test each other

The Electron – History/Theory Discovery #: 1st subatomic particle discovered Discovered by JJ Thomson in 1897 JJ Made a CRT (cathode ray tube) and found that when he shot electricity through it a beam of light appeared The beam of light was affected by magnetic & electric forces (does light do that??) He proposed that it wasn’t light but tiny, negatively charged particles he called electrons (btw: he thought the discovery was useless)

Thomson’s Model The atom was Neutral in charge so… Most of the atom was a diffuse positively charged “goo” or matrix Electrons were tiny particles that floated around in the “goo”. Electrons were very tiny compared to the mass of the atom

The Thomson Plum Pudding Model 1897 – The Plum Pudding Model I prefer the “Chocolate Chip Cookie Dough Model negative electrons positive matrix or goo that made up the rest of the atom

Atomic Particles The Proton

The Proton – Fun Facts Abbreviated p+ Gives the nucleus a positive charge Gives the element its unique characteristics & identifies the element (# p + is unique to each element Structure: Hadron (composite particle made of smaller particles) Mass = 1 amu* Charge: Positive Location: Nucleus

The Proton on the Periodic Table How many protons are there in an element?? Where do you find it??? 20 Ca Calcium 40.078 # of p+ = Atomic Number Let’s make a note on our PT & test each other

The Proton – History/Theory Discovery #: 2nd subatomic particle discovered Discovered by Ernest Rutherford in 1918 Rutherford first proposed the positive nucleus in 1911 from the “Gold Foil Experiment” changing the model of the atom again http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

Rutherford’s Models The nucleus was Very dense Had most of the mass of the atom Was positive Very, very tiny compared to the entire atom Atoms are mostly empty space The electrons move around the outside of the nucleus Rutherford model – nuclear model – kind of like a plasma ball w/ a tiny positive nucleus and electrons floating around outside it Discovered the proton later in the first nuclear reaction How tiny? 400 x tinier than this – and that’s only the nucleus!!! Protons are smaller yet!!!!

The Rutherford (Nuclear) Models 1911 Model with just a positive nucleus in the center of the electrons 1918 Model with protons making up the nucleus

Atomic Particles The Neutron

The Neutron – Fun Facts Abbreviated n0 Adds mass to the nucleus Helps hold the nucleus together (prevents proton repulsion from destroying the nucleus) Structure: Hadron (composite particle made of smaller particles) Mass = 1 amu* Charge: Neutral (no charge) Location: Nucleus

The Neutron on the Periodic Table How many neutrons are there in an element?? Where do you find it??? 20 Ca Calcium 40.078 #n0 is NOT found on the PT More on this later

The Neutron – History/Theory Discovery #: 3rd subatomic particle discovered Discovered by James Chadwick (also a student of JJ Thomson) in 1936 – (Rutherford said it should be there, Chadwick gave them evidence) Chadwick produced a beam of neutral particles that knocked protons out of paraffin wax https://www.youtube.com/watch?v=HnmEI94URK8 Led to the development of the atomic bomb

Chadwick’s Model Similar to the current model with p+ & n0 in the nucleus and e- orbiting the nucleus in the electron cloud

Atomic Particles Isotopes & The Neutron

Isotopes & the Neutron Isotopes: Atoms of the same element with different numbers of neutrons The number of neutrons can be different in an element (that’s why there is no neutron number on the PT) The number of neutrons must be calculated for each isotope Example: Magnesium has 3 isotopes Symbol #p+ #n0 #e- Mg - 24 12 12 12 Mg - 25 13 Mg - 26 14

Isotopes & Mass Number Mass number (mass #) is the number of p+ & no in a specific isotope of an element Mass # = #p+ + no or #no = Mass # - #p+ Lets put this on the PT somewhere

Isotopes & Mass Number #1 How do you know which isotope you have?? Mass # is found in one of 2 ways – prioritized list Isotope Notation (given to you with the element symbol) – 100% accurate Mass # Element Symbol C-14 Mass # OR 14 6 C Element Symbol Atomic # So in C-14 there are… 6 p+ & 6 e- (atomic number of C is 6) 8n0 (Mass # - # p+ = #n0 or 14 - 6 = 8 )

Practice Isotope Notation Isotope Symbol # p+ #n0 #e- O-18 N-15 Si-30 Cl-37 K-41 Fe-54 Ni-62 Cu-65 Br-79 8 10 8 7 8 7 14 16 14 17 20 17 19 22 19 26 28 26 28 34 28 29 36 29 35 44 35

Isotopes & Mass Number #2 How do you know which isotope you have?? 2. MCI (most common isotope) –50% accuracy Round the Average Mass to a whole number to get mass # for the m.c.i. Average mass = 40.078 amu so…. round it and … The mass number of the most common isotope is 40 so Ca-40 20 Ca Calcium 40.078 5 B Boron 10.806 Average mass = 10.806 amu so…. round it and … The mass number of the most common isotope is 11 so B-11

Average Mass

Practice M.C.I. method Isotope Symbol # p+ #n0 #e- O N Si Cl K Fe Ni Cu Br 16 (avg mass = 15.999) 8 8 8 14 (avg mass = 14.006) 7 7 7 28 (avg mass = 28.084) 14 14 14 35 (avg mass = 35.446) 17 18 17 39 (avg mass = 39.098) 19 20 19 56 (avg mass = 55.845) 26 30 26 59 (avg mass = 58.693) 28 31 28 64 (avg mass = 63.546) 29 35 29 80 (avg mass = 79.904) 35 45 35

Sample Formats Carbon - 12 Carbon - 13 Carbon - 14 Isotope Name 6 6 6 6 7 8 Isotope Name Isotope Symbol # p+ # n # e- Lithium – 6 Li – 6 Lithium – 7 Li – 7 Iron – Fe – 28 Fe- 31 Chlorine Mercury 3 3 3 3 4 3 54 26 26 57 26 26 Cl - 35 17 18 17 Hg - 200 80 120 80

Atomic Particles The Electron Cloud

Atomic Structure – electron cloud Nucleus 1st Energy Level: holds up to 2 e- The region of the atom around the nucleus where the electrons are located Makes up most of the atom’s size Mostly empty space Made up of energy levels that e- can move in and out of by absorbing & releasing energy e- absorb energy and move to higher levels or release energy and drop back to lower levels 2nd Energy Level: holds up to 8 e- 3rd Energy Level: holds up to 18 e- 4th Energy Level: holds up to 32 e- Formula: ?? Skip valence e- for now

Atomic Theory – Electron Cloud Energy levels were proposed by Neils Bohr in 1913 His data supported that e- absorb heat/electrical energy & then release the energy as certain colors of light He concluded that e- orbited the nucleus in energy levels Jumped to higher levels when absorbing energy Released light energy when they fell back down https://www.youtube.com/watch?t=175&v=CUk3enr-m0w

Atomic Model– Bohr Model Neils Bohr’s model is sometimes called the planetary model but we usually call it the… Bohr Model light released e.l. = 3 e.l. = 2 e.l. = 1 Time for a demo

Electron Cloud – Later Discoveries In 1926 Erwin Schrodinger & Max Born proposed that electrons actually behaved more like waves than particles and therefore proposed the wave model. Schrodinger is famous for his “Schrodinger’s Cat” example used to explain this model The quantum mechanical model of the electron cloud is our current model and many scientists have contributed to its development. discovered e- exist within orbitals, which are not circular, within the energy levels dark, shaded areas of the cloud are more likely to contain e-