The Structure of Atoms Chapter 4 Section 2

Standards Standard 1: Matter #2 Describe the structure and arrangement of atomic particles.

Objectives List differences between protons, neutrons, and electrons Explain what is unique about atoms and how ions are formed Tell how many protons, neutrons and electrons are in an atom Define isotopes and explain why they have different atomic masses Explain how the mole is used in chemistry Convert between moles and grams Calculate molar mass of compounds

The GREAT Trio Atoms are made of three major subatomic particles These are distinguished by mass, charge, and location ParticleChargeLocationMass (kg) Proton PositiveNucleus1.67 × NeutronNeutralNucleus1.67 × ElectronNegative Electron Cloud 9.11 × Objective 1: List differences between protons, neutrons, and electrons

Objective 2: Explain what is unique about atoms and how ions are formed Unique is the Way!! All elements have a unique number of protons Defines the element IF an atom has equal numbers of protons and electrons the atom is NEUTRAL!! IF the atom has more electrons than protons the atom is A negative ION – aNion! IF the atom has more protons than electrons the atom is A positive ION - ca + ion Three forces hold atoms together Weak nuclear, strong nuclear, and electromagnetic!

Some ImPoRtAnT NuMbErS!! Atomic Number Tells how many PROTONS are in the nucleus Tells how many ELECTRONS in a neutral atom Designated by A So…What is A for Carbon?? Hydrogen?? Mass Number Equals the number of PROTONS + NEUTRONS Designated by M Atoms of each element have the same number of protons, but can have different numbers of neutrons as well as electrons!! Atoms of each element have the same number of protons, but can have different numbers of neutrons as well as electrons!! Objective 3 : Tell how many protons, neutrons and electrons are in an atom Objective 3: Tell how many protons, neutrons and electrons are in an atom

So…What BOUt the NEUTRON!! Symbols for the elements are usually written in the form of M= mass # A= atomic # Sm = Symbol of element Getting # of neutrons is simple.. All we do is subtract M from A How do we know how many protons and electrons are in the atom? LOOK at ATOMIC NUMBER! For PROTONS and ELECTRONS in a NEUTRAL atom! For ions ELECTRONS are found by subtracting (cation) or adding (anion) the CHARGE from/to the atomic number Example…uranium-235 Objective 3 : Tell how many protons, neutrons and electrons are in an atom Objective 3: Tell how many protons, neutrons and electrons are in an atom

Weirdo Atoms… IsOtOpEs Element with same # of protons but DIFFERENT number of NEUTRONS These have different masses than the other atoms of a particular element Their chemical and physical properties do NOT change Written as name of element – mass number Example – Uranium 235 Hydrogen has 3 isotopes with DIFFERENT names! Hydrogen – 1 (Hydrogen) Hydrogen – 2 (Deuterium) Hyrdrogen – 3 (Tritium) How many protons does each isotope of hydrogen have? How many neutrons does each isotope of hydrogen have? Objective 4: Define isotopes and explain how they make up the atomic mass of an element

Atomic Mass… Atomic masses are weighted average It’s the average of the masses of all the isotopes of an element Unit is the unified atomic mass unit (u) Based on carbon – 12 (1/12 the mass of carbon – 12) Makes working with small masses EASIER! We can find the most common isotope of an element by looking at the atomic mass We just round the atomic mass! Objective 4: Define isotopes and explain how they make up the atomic mass of an element

Moles and Counting Because chemists deal with LARGE #s of small particles They use a very LARGE counting unit called the mole 1 mole = 602, 213, 670, 000, 000, 000, 000, 000 particles This number is usually written as × particles/mole Usually called Avogadro’s number Moles and grams are related!! The mass of one mole of a substance is called the molar mass! Equals the atomic mass expressed in g/mol Ex. 1 mole of carbon-12 = g!! Also expressed as g/mol Objective 5: Explain how the mole is used in chemistry

Compounds Have Molar Masses TOO!! All we have to do is add up the molar masses of the atoms combined in the compound! Must know number of atoms as well as their masses! If there are SUBSCRIPTS by the element you MULTIPLY the subscript by the molar mass of the element! Ex: What is the molar mass of water? What is the molar mass of carbon dioxide (CO 2 ) Objective 6: Calculate the molar masses of compounds

We Can Convert Between Moles and Grams!! Molar Masses help us to convert (change) Moles into grams or grams into moles! How to convert grams into moles Divide by molar mass! How to convert moles into grams Multiply by molar mass! Examples: What is the mass in grams of 5.50 mol of iron? How many moles are in 5.47 g of fluorine? Objective 7: Convert between moles and grams

T – Charts for Converting! Moles to grams Grams to moles: GivenUnknown MolesMolar mass (g) Moles GivenUnknown GramsMoles Molar mass (g)