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 is an isotope? Agenda for Thursday Dec 16 th 1.Isotopes practice 2.Valence Electrons 3.Lewis Dot Structures

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 For each isotope, give the number of protons, electrons, and neutrons: C-14 _________ p _________e ___________n Zn-65 _________ p _________e ___________n Na-21 _________ p _________e ___________n Be-8 _________ p _________e ___________n S-31 _________ p _________e ___________n

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

Electrons and Energy Levels Electrons with different amounts of energy exist in different energy levels Many possible energy levels an electron can occupy Number of energy levels depends on the number 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

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. 6P 6N

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!

About Lewis Dot Structures Gilbert Newton Lewis – American chemist Proposed the idea of Lewis Dot Structures – use the element’s symbol and small dots to represent the valence electrons present in a specific atom

Lewis dot structures Lewis dot structures are a way to draw atoms showing only the valence electrons the symbol for the element is used to represent the atom and its core electrons Ca

Remember this? It makes life easy now

Lewis dot structures Used to show valence electrons Start with single electrons on all four sides first before starting to pair up N

You try Ne C O Cl

Bonding potential Unpaired electrons are used in chemical bonds. How many bonds can Nitrogen have? 3 unpaired electrons  3 potential bonds N

Let’s try one together K How many valence electrons does potassium have?

One more example Rn What element is Rn? Radon How many valence electrons does Rn have?