Outline the history of the atomic model. Agenda for Tuesday Dec 14 th 1.Atoms 2.Atomic mass, #, protons, etc
Atoms Nucleus in the center – Protons and neutrons Electrons on outside of nucleus – Electron cloud model – Electrons exist in energy levels – based on # of electrons
Atomic Number and Atomic Mass B boron Element name Atomic number Symbol Atomic mass
Atomic number: # of protons in nucleus Each element has a different atomic # Identifies the element Hydrogen = smallest atomic # (1) # of protons = # of electrons
Atomic mass: total mass of protons and neutrons in an atom, measured in atomic mass units (amu) – Atomic weight Atoms of the same element can have different numbers of neutrons - isotopes # on periodic table is the average atomic mass for that element
We will round the average atomic mass to get a whole # called the mass number. Examples: Sodium (Na) Avg. atomic mass = amu Mass # = 23 Nitrogen (N) Avg. atomic mass = amu Mass # = 14
Finding # of neutrons mass # - atomic # = # of neutrons For Na: 23 – 11 = 12 neutrons For N: 14 – 7 = 7 neutrons
Practice
Find the mass number, protons, neutrons, and electrons for Bromine. Agenda for Wednesday Dec 15 th 1.History of the Atom Flash Cards 2.Practice with mass, protons, etc 3.Isotopes
Element Name Atomic Number Number of Protons Number of Neutrons Mass Number carbon12 88 hydrogen1 614 hydrogen2 nitrogen Oxygen Carbon
Isotopes Atoms of the same element can have different numbers of neutrons isotopes # of protons and electrons stays the same for a particular element – Mass changes – Means # of neutrons changes Atomic mass on your P.T. is an average of all the isotopes For Boron:.8 (10 amu) +.2 (11 amu) = amu
More on Isotopes Because the numbers of neutrons in the isotopes are different, the mass numbers are also different You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11
Example: – Neon. All neon atoms have 10 protons and 10 electrons. Some neon atoms have 10 neutrons and some have 12. – Both isotopes of neon
Ne or Ne-20 Ne or Ne Atomic # (# of protons) Mass # (protons + neutrons). Different for each isotope
What’s the point of Isotopes You can tell how old something is – Radiocarbon Dating Use as markers in research – Follow a certain molecule, atom
Practice Problems You will need your periodic table! 1.For Mg-25: How many protons, electrons, and neutrons? 2.For N-15: How many protons, electrons, neutrons? 3.For P-31: How many protons, electrons, neutrons?
Practice
What is an isotope? Agenda for Thursday Dec 16 th 1.Mass #, Atomic weight, proton review 2.Valence Electrons 3.Lewis Dot Structures
Atoms Nucleus in the center – Protons and neutrons Electrons on outside of nucleus – Electron cloud model – Electrons exist in energy levels – based on # of electrons
Valence Electrons Electrons in the outermost energy level Valence electrons determine reactivity and other chemical properties 8 valence electrons means a stable atom = do not want to react with other atoms
Where are electrons found? Nucleus Least likely Most likely
13 p + 14 n 0 Help! We’re so vulnerable! Valence electrons A way to draw an atom showing where electrons are found
Valence electrons Carbon -12 has 4 electrons in the last energy level... therefore carbon-12 has 4 valence electrons
Bohr’s Model Nucleus 1 st shell can hold 2 e - 3 rd shell can hold 8 e - 2 nd shell can hold 8 e -
How many electrons in each shell? 1 st shell = 2 electrons 2 nd shell = 8 electrons 3 rd shell = 8 electrons 4 th shell = 18 electrons
Drawing Carbon-12 with Bohr’s Model Steps: 1.Find number of neutrons and protons. 2. Find number of electrons. 3. Fill in electrons, beginning with the 1 st energy level.
How many valence electrons does Nitrogen have? NUCLEUS
How many valence electrons does Calcium have? Calcium has 2 Valence electrons NUCLEUS
How many valence electrons does Phosphorous have? Phosphorous has 5 Valence electrons NUCLEUS
How many valence electrons does Boron have? NUCLEUS Boron has 3 Valence electrons
Cool Trick!