The Atom & Periodic Table

1. The Atom & Periodic Table How were atoms discovered? What are atoms made of? How is the Periodic Table arranged?

3. Atoms and the Periodic Table • Atom “Atomos” (Greek) – smallest piece of matter that still retains those properties • Matter – anything that has mass and volume, what all material is made up of • Model – uses familiar ideas to explain unfamiliar facts observed in nature

4. Models of the Atom1) Greek Model • 1) Search for a description of matter began with a Greek philosopher Democritus more than 2400 years ago • He thought that matter was divided over and over – would eventually result in something so small that it couldn’t be divided any longer • He named this smallest particle of matter the Atom.

5. 2) Dalton’s Model • Early 1800’s English Chemist John Dalton did several experiments that led to the acceptance of the atom • Dalton’s Atomic Theory – 1803 • All elements are composed of Atoms, they are indivisible and indestructible particles. • Atoms of same elements are exactly alike. • Compounds are formed by the joining of Atoms or two or more elements • *This theory became one of the foundations of chemistry

6. 3) JJ Thompson • Electrons – negatively charged particles • If there were negative particles he concluded there had to be positive particles to balance it out • Plum Pudding Model • Negatively charged ‘plums’ • Positively charged ‘pudding’

7. 4)Ernest Rutherford • Gold Foil Experiment – (led to downfall of Plum Pudding Model) • Discovered the proton by shooting small alpha particles through a thin sheet of gold, some were reflected • Gives us the “Planetary Model” where particles surround the small, dense positively charged center

9. 5) Niels Bohr • 1913, Danish Scientist – thought the negatively charged electrons have a definite orbit around the nucleus – much like the planets revolve around the sun • Led to the development of … • Electron Cloud Theory: electrons are everywhere but nowhere around the nucleus

10. Antonius Van den Broek, 1913 – The atomic number in nuclear charge • Henry Moseley, 1913 – English Physicist who proved Rutherford’s theory through experiments and refined the field of X-ray diffraction • James Chadwick, 1932 – discovered the neutron • Cyclotron – allowed for the creation of new elements heavier than uranium

11. 6) Wave model • Today’s atomic model is based on wave mechanics- electrons don’t move in an orbital but bounce around in a distinct area • The location of the electron depends on how much energy it has • Theory of today says that each atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make the atom neutral – a happy atom!

12. Parts of an Atom

13. Sub Atomic Particles • Proton: • positively charged particle • All protons stay the same and cannot leave • Protons determine the identity of the atom • Neutron: • Electrically neutral particle, provides mass • Number of these can change – gives us isotopes

14. Sub Atomic Particles • Electrons: • In a neutral atom ( no charge) the number of negatively charged particles is equal to the number of positively charged particles • Electron Cloud – space in which electrons are likely to be found, move so fast and are so small we can’t see them. • Ions occur when there is an imbalance between protons and electrons, e- are the one that can move

15. Quarks – sub, sub-atomic • There are six types of quarks, or flavors- • Up, down, strange, charm, bottom and top • They combine to form hadrons – the most stable of these are protons and neutrons

16. Forces within an Atom • Electromagnetic force- can attract or repel particles (depending on their charge), this is what keeps them in their orbital • Strong force – opposes the EM force of repulsion between protons • Strongest but has limited range, only when protons are very close together • Weak Force – responsible for a process known as radioactive decay • Decay – a neutron in the nucleus changes into a proton and an electron • Gravity- weakest force in nature

17. Atomic Identity • Atomic Number • The number of protons in the nucleus of an atom • This number stays the same among all atoms of the same element • Similar to your SSN • Atomic Mass • Sum of the protons and neutrons in the nucleus of an atom, deals with one atom at a time • Similar to your weight, it can change • Average Atomic Mass • Average of all isotopes of an element in existence, Deals with more than one atom • AMU – mass unit or amu (6 with 23 zeros equal 1 gram)

18. Isotopes vs. Ions Isotopes Ions • Isotopes are atoms with a different mass due to different number of neutrons. • Average Atomic Mass is an average of all occurring isotopes (this is why there is a decimal on some) • An Ion is an electrically charged atom • Ions deal with the charge or oxidation number • How?Gain/Lose e-

19. 8 -2 O oxygen • Atomic # (AN or Z) • Symbol • Name • Atomic Mass (AMU) • Pos/Negnumber at top tells the charge – deals with ions 15.99

20. Quiz… • What is the symbol for Lead? • What is the atomic number of Potassium? • What is the atomic mass of a Carbon atom? • What is the average atomic mass of Aluminum? Why isn’t it exactly double the number?

21. Hydrogen isotopes • Protium Deuterium Tritium

22. A X Mass Number Element Symbol Z Atomic Number 2 3 1 H (D) H (T) H 1 1 1 235 238 U U 92 92 Atomic number (Z) = number of protons in nucleus Mass number (AMU) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in the nucleus 2.3

23. Examples

24. Ex) Carbon

25. Octet Rule • The outer shell of an atom can hold only a certain amount of electrons • 1st shell holds up to 2 e- • 2nd shell holds up to 8 e- • 3rd shell holds up to 8 e- • 4th shell holds up to 18 e- • 5th shell holds up to 32 e- • Since we only study the first few rows, we say the atom can hold up to 8 – hence, Octet Rule

26. Electron Orbitals – s p d f orbitals

27. Compounds and Molecules Diatomic molecules Binary Compounds: Covalent and Ionic Bonds Polyatomic Compounds Naming and Balancing

28. H2 H2O NH3 CH4 A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds, electrons are key to this DiatomicMolecules: contains only two atoms, short list of elements that buddy up – not stable enough alone H2, N2, O2, Br2, Cl2, I2, F2 A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4 2.5

29. 11 protons 11 electrons 11 protons 10 electrons Na+ Na 17 protons 18 electrons 17 protons 17 electrons Cl- Cl An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. 2.5

30. 2.6

31. molecular empirical H2O A molecular formulashows the exact number of atoms of each element in the smallest unit of a substance An empirical formulashows the simplest whole-number ratio of the atoms in a substance H2O CH2O C6H12O6 O3 O N2H4 NH2 2.6