Atoms and their structure Unit 3 Atoms and their structure

Modern View The atom is mostly empty space Two regions Nucleus - protons and neutrons Electron cloud - region where you might find an electron

Density and the Atom Since most of the particles went straight through the gold foil, the atom was mostly empty space Because the alpha particles turned so much, the positive particles must have been heavy Small volume and big mass = big density. This small dense positive area is the nucleus

Subatomic particles Electron – located outside of nucleus, has negative charge Proton - positively charged particles inside of nucleus that are many times heavier than the electron Neutron - no charge but about the same mass as a proton, located inside of nucleus

Subatomic particles Relative mass (amu) Particle Name Actual mass (g) Symbol Charge Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron n0 1 1.67 x 10-24

Structure of the Atom There are two regions The nucleus With protons and neutrons Positive charge Almost all the mass Electron cloud - most of the volume of an atom The region where the electron can be found

Size of an atom Atoms are small Measured in picometers, 10-12 meters Hydrogen atom, 32 pm radius Nucleus is very tiny compared to atom If the atom was the size of a stadium, the nucleus would be the size of a marble Radius of the nucleus is near 10-15 m Density near 1014 g/cm3

Counting the Pieces Atomic Number = number of protons # of protons determines kind of atom the same as the number of electrons in the neutral atom Mass Number = the number of protons + neutrons Includes all the particles with mass NOT found on the periodic table

What about when Electrons ≠ Protons Electrons may be gained or lost Gaining electrons gives a negatively charged ion called an anion Losing electrons gives a positively charged ion called a cation

What about when Electrons ≠ Protons Practice with ions… Magnesium makes ions with a 2+ charge. Are electrons lost or gained? How many electrons are moved? Fluorine makes ions with a 1- charge. Are electrons lost or gained? How many electrons are moved? An ion has 13 p+ and 10 e-. Give the symbol and charge for the ion. An ion has 34 p+ and 36 e-. Give the symbol and charge for the ion.

Isotopes Dalton was wrong Atoms of the same element can have different numbers of neutrons different mass numbers (will have the same atomic number called isotopes

X Symbols for Isotopes Mass number Atomic number Nuclear Notation Contains the symbol of the element, the mass number and the atomic number X Mass number Atomic number

Symbols for Isotopes carbon- 12 carbon -14 uranium-235 Hyphen Notation Contains the symbol (or name) of the element and the mass number. carbon- 12 carbon -14 uranium-235

Na Symbols for Isotopes 24 11 Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name 24 Na 11

Br Symbols for Isotopes 80 35 Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name 80 Br 35

Symbols for Isotopes if an element has an atomic number of 34 and a mass number of 78 what is the number of protons number of neutrons number of electrons Symbol – Nuclear & Hyphen notation Name

Symbols for Isotopes if an element has 91 protons and 140 neutrons what is the Atomic number Mass number number of electrons Symbol – Nuclear & Hyphen notation Name

Symbols for Isotopes if an element has 78 electrons and 117 neutrons what is the Atomic number Mass number number of electrons Symbol – Nuclear & Hyphen notation Name

Atomic Mass How heavy is an atom of oxygen? There are different kinds of oxygen atoms More concerned with average atomic mass Based on abundance of each element in nature Don’t use grams because the numbers would be too small

Atomic Mass Is not a whole number because it is an average are the decimal numbers on the periodic table

Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom 6 p+ and 6 n0 Each isotope of an element has its own atomic mass we get the average atomic mass of an element using weighted averages (need mass & percent abundance)

Calculating averages You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks? Total mass = (4 x 50) + (1 x 60) = 260 g Average mass = (4 x 50) + (1 x 60) = 260 g 5 5

Calculating averages (% as decimal x mass) + (% as decimal x mass) + … If 80% of the rocks were 50 grams and 20% of the rocks were 60 grams what is the weighted average mass of the rocks? Weighted Average = (% as decimal x mass) + (% as decimal x mass) + … (0.8 x 50 g) + (0.2 x 60 g) = 52 g

Homework – due 10/18 Pg 76 (#3) Pg 87 (#2-3) Qs with * need to have answers in the form of complete sentences. Please show your math work as well.