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•Draw a detailed picture of Draw a detailed picture of an atom. (Think about what an atom. (Think about what you may have learned in you may have learned in middle school. What makes middle school. What makes up an atom?) up an atom?)

Atoms: The Building Atoms: The Building Blocks of MatterBlocks of Matter

Chapter 3Chapter 3

Atoms, Compounds & Atoms, Compounds & MoleculesMolecules

• Atoms: the Atoms: the smallestsmallest particle of an element particle of an element that retains the chemical properties of that that retains the chemical properties of that element.element.

• Compound: a substance that consists of two Compound: a substance that consists of two or more or more differentdifferent types of elements. types of elements.

• Molecule: a substance that consists of two or Molecule: a substance that consists of two or more more atomsatoms. .

• Ion: An atom or molecule with a net Ion: An atom or molecule with a net electricelectric charge due to the loss or gain of electrons.charge due to the loss or gain of electrons.

Dalton: Basic Atomic Dalton: Basic Atomic TheoryTheory

1.1.All All matter is matter is made of made of atoms.atoms.

2. 2. Atoms of one element differ Atoms of one element differ in in propertiesproperties (size, mass etc…) (size, mass etc…) from atoms of another element.from atoms of another element.

3. Atoms of different elements 3. Atoms of different elements combine in simple, combine in simple, whole-whole-number number ratios to form ratios to form molecules.molecules.

4. In chemical reactions atoms can 4. In chemical reactions atoms can combine, combine, separateseparate and rearrange, and rearrange, but not destroyed.but not destroyed.

Structure of the AtomStructure of the Atom

• Atoms consist of two Atoms consist of two regions:regions:

1.1.NucleusNucleus: Which is a very : Which is a very small small region located in the region located in the center of an atom which center of an atom which contain positively (+) contain positively (+) charged particles called charged particles called protonsprotons and one or more (=) and one or more (=) neutral particles called neutral particles called neutronsneutrons..

2.2.Electron cloud: Electron cloud: A region A region very very largelarge compared to the compared to the nucleus which contains very nucleus which contains very small negatively (-) charged small negatively (-) charged particles called particles called electronselectrons..

Structure of the AtomStructure of the Atom

• Neutrons, protons Neutrons, protons and electrons are and electrons are called the called the subatomicsubatomic particles.particles.

• ElectronsElectrons are much are much smaller in size and smaller in size and mass than mass than neutrons and neutrons and protons. protons.

Discovery of the Discovery of the ElectronElectron

• Cathode-ray tube Cathode-ray tube experiments performed by experiments performed by JJ Thompson provided evidence that JJ Thompson provided evidence that all all atoms atoms contained negatively charged particles.contained negatively charged particles.

Questions raised by the discovery of the Questions raised by the discovery of the electron electron

• If it is true that all atoms have these super If it is true that all atoms have these super tiny negatively charged particles two main tiny negatively charged particles two main questions arise:questions arise:

1.1.Because atoms are electrically Because atoms are electrically neutralneutral, they , they must contain a positive charge to balance out must contain a positive charge to balance out negative negative electronselectrons

2.2.Because electrons have so much Because electrons have so much lessless mass mass than atoms, atoms must contain other than atoms, atoms must contain other particlesparticles that account for most of their mass. that account for most of their mass.

Discovery of the Atomic Discovery of the Atomic NucleusNucleus

• Rutherford discovered that all atoms have a very Rutherford discovered that all atoms have a very small, small, densedense and positively charged nucleus by and positively charged nucleus by performing what we call the “performing what we call the “goldgold foil experiment.” foil experiment.”

Rutherford’s Rutherford’s ConclusionsConclusions

• Most of the Most of the massmass and all of the and all of the positivepositive charge of the atom is in a very dense nucleus.charge of the atom is in a very dense nucleus.

• However the nucleus only takes up a very However the nucleus only takes up a very smallsmall space in an atom. space in an atom.

• Atoms are mostly Atoms are mostly empty spaceempty space..

EXAMPLE: If the nucleus of an atom was the EXAMPLE: If the nucleus of an atom was the size of a size of a marblemarble, the size of the , the size of the atomatom would would be equal to a football field. be equal to a football field.

Atomic NumberAtomic Number

• Atomic Number: (Z) tells you how many Atomic Number: (Z) tells you how many protonsprotons are in each atom of an are in each atom of an elementelement. The atomic # . The atomic # identifies identifies the element.the element.

• Chemical (Atomic) Symbol: Is the Chemical (Atomic) Symbol: Is the letterletter abbreviation for an abbreviation for an element.element.

Atomic Number = 6

Chemical Symbol

Examples!Examples!

• How many protons are in each of the following:How many protons are in each of the following:

From yesterday…From yesterday…

•Which 2 subatomic particles did Which 2 subatomic particles did we say are the biggest/ make up we say are the biggest/ make up most of an atom’s mass?most of an atom’s mass?

Mass NumberMass Number

• Mass Number: (A) is the total number of Mass Number: (A) is the total number of protonsprotons and and neutronsneutrons that make up the nucleus of an atom. that make up the nucleus of an atom.

• Mass Number (A) – Atomic Number (Z) = Number of Mass Number (A) – Atomic Number (Z) = Number of NeutronsNeutrons

Mass Number can be written two ways:Mass Number can be written two ways:

Be Able to InterpretBe Able to Interpret

With your group…With your group…

•Can the atomic number ever be Can the atomic number ever be bigger than the mass number? bigger than the mass number? Why or why not?Why or why not?

Example!Example!

• How many protons, neutrons, and electrons are in Carbon 14?

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• Why are isotopes important?Why are isotopes important?

isotopesisotopes

• Isotopes: are atoms of the Isotopes: are atoms of the samesame element that element that have different have different masses. masses.

• Isotopes of a particular element all have the Isotopes of a particular element all have the same number of same number of protonsprotons and and electronselectrons, but , but different numbers of different numbers of neutronsneutrons..

Reading IsotopesReading Isotopes

Average Atomic MassAverage Atomic Mass

• Although Although isotopesisotopes have different masses, they have different masses, they do not differ significantly in their do not differ significantly in their chemicachemical l behavior.behavior.

• Average atomic mass: the Average atomic mass: the weightedweighted average average of the atomic masses of the naturally of the atomic masses of the naturally occurring isotopes of an occurring isotopes of an element.element.

• Basically two things matter: the Basically two things matter: the massmass and and relativerelative abundance of an elements isotopes. abundance of an elements isotopes.

NitrogenNitrogen

• A sample of A sample of nitrogen is tested nitrogen is tested and has a two and has a two isotopes of nitrogen. isotopes of nitrogen. 99.64% of atoms 99.64% of atoms are N-14 and 0.36% are N-14 and 0.36% atoms are N-15. atoms are N-15. What is the average What is the average atomic mass?atomic mass?

ionsions

• An An ionion is an atom or a molecule in which the is an atom or a molecule in which the total number of electrons IS NOT EQUAL to total number of electrons IS NOT EQUAL to the number of protons. This gives the atom or the number of protons. This gives the atom or molecule a net positive or negative molecule a net positive or negative ELECTRICAL CHARGE. ELECTRICAL CHARGE.

CATIONCATION

• If a neutral atom loses one or more electrons, If a neutral atom loses one or more electrons, it has a net POSITIVE charge, and is called a it has a net POSITIVE charge, and is called a CATION.CATION.

anionanion

• If an atom gains electrons, it has a net If an atom gains electrons, it has a net NEGATIVE charge and is called an NEGATIVE charge and is called an ANION. ANION.

Who Cares?Who Cares?

• A lithium-ion battery is a rechargeable battery used in lots of cell phones and cameras. Lithium ions move from the negative electrode to the positive electrode during discharge and back when charging.