Atoms and the Periodic Table

Matter Matter is everything around you that has mass. Anything you can see, touch, taste, or smell is matter! Air Desks People Soil Plants What is it that makes up matter?!

Matter What is matter made of? Is it all the same? Democritus (460 B.C. - 370 B.C.) was a Greek philosopher believed the universe was mostly empty space and tiny bits of stuff. He didn’t know what the stuff was but he knew it must be REALLY small! So small it could not be broken into anything smaller

The Chalk Conundrum! If you break a piece of chalk in half…is it still chalk? When is it no longer chalk?

Can you make matter? Democritus never explained where matter came from or where it could go People just guessed that matter could change into different types of matter

Matter cannot be created or destroyed! Can you make matter? Matter cannot be created or destroyed! If a space shuttle leaves Earth with astronauts and food and water and air weighing 10,000 lbs. it will return weighing 10,000 lbs.

Matter Atom – small particle that makes up matter Atom in Greek means “cannot be divided”

Parts of an Atom Protons – positive charged particle Atoms are made of only 3 different things Protons – positive charged particle Neutrons – particle with no charge Electrons – negatively charged particle Nucleus – center of the atom made up of protons and neutrons Protons and neutrons are found in the nucleus or center of the atom Electrons are found outside the nucleus

Parts of an Atom Electrons are so small as it is we hypothesize that they aren’t made up of anything smaller Protons and neutrons however… Quarks – smaller particles that compose protons and neutrons of an atom 6 unique quarks have been discovered It took almost 450 scientists several years to discover the 6th quark!

How big are Atoms? SMALL! Really, really, really, really, small…

The Atomic Model So what exactly does an atom look like?! Scientists have developed models over the years to explain how atoms work…

Gold Foil Experiment Rutherford was one of the first to propose that atoms had a dense nucleus Gold foil experiment Particles were fired at a piece of gold foil Most went straight through Some were deflected

Electron Cloud Model By 1926, scientists had developed the electron cloud model of the atom Electrons do not follow fixed orbits Instead they occur frequently in certain areas around the nucleus at any given time

What is in an Atom?

Bohr Model Orbital – each ring of electrons in an atom The Bohr model represents an atom by using rings drawn around the nucleus with dots to represent electrons Orbital – each ring of electrons in an atom The 1st orbital can only hold 2 electrons! The following orbitals can only hold a maximum of 8 electrons

Atoms Element – a known substance that cannot be broken down into another substance Made of only one kind of atom Sulphur (S) Potassium (K) Aluminum (Al) Chlorine (Cl)

Periodic Table Periodic Table – a chart that organizes elements by the number of protons they have in the nucleus Elements are listed by their chemical symbols Aluminum = Al Calcium = Ca Gold = Au Oxygen = O Hydrogen = H Carbon = C

How to Read a Periodic Table Dimitri Mendeleev, a Russian Chemist, developed the first periodic table Mendeleev based his table on the mass of the atoms “I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.” A British chemist later improved upon the periodic table by rearranging the elements based on their atomic number (the number of protons).

Atomic Number Atomic number – the number of protons found in a single atom of the element The periodic table is arranged based on these numbers

Atomic Mass If you were asked how tall you were, would you answer in kilometers? NO! You would use an appropriate unit! (cm, or m) Scientists had to develop an appropriate unit for the mass of atoms since they were so tiny! Atomic mass unit (amu) – unit of measure used for atomic particles Atomic mass – the mass of an atom of the element

Atomic Mass How do we calculate the atomic mass? 1 proton is equal to almost exactly 1 amu 1 neutron is equal to almost exactly 1 amu Electrons are so tiny they make little difference

How Many Neutrons? The number of protons in an atom is equal to the element’s atomic number The number of electrons in a neutral atom are equal to the number of protons 1 positive and 1 negative equals 0! Often, the number of neutrons is equal to the number of protons but NOT ALWAYS!

How Many Neutrons? Krypton Has an atomic number of 36 Number of protons? Number of electrons? Number of neutrons? Round the atomic mass to the nearest whole number 83.80  84 84 – 36 protons = 48 36 36

Reading a Periodic Table All the rows read from LEFT to RIGHT Each row is called a period The period an element is in tells you how many electron orbitals are present Elements in the top period have 1 orbital Elements in the 3 period have 3 orbitals

Reading a Periodic Table The vertical columns of the periodic table are called groups Elements found in the same group have the same number of electrons in their outer orbital Valence Electrons – the electron in the outermost ring of an atom Elements in group 1 have 1 electron in their outer shell Elements in group 4 have 4 electrons in their outer shell The middle “transition elements” don’t follow this rule! We’ll talk about them later on…

Try it! Nitrogen Atomic number? Number of protons? 7 Number of electrons? Number of neutrons? Atomic mass? Number of valence electrons? 7 7 7 7 14 7

Isotopes Not all atoms of an element have the same number of neutrons! Isotope – an atom of an element that has a different number of neutrons Still have the same number of electrons and protons Still the same element Only difference is the mass!

Isotope Isotopes of elements are indicated by their mass number The average atomic mass of an element is the weighted-average mass of all isotopes 4 of 5 atoms of B have 6 neutrons 1 of the 5 have 5 neutrons 4 5 (11 amu) + 1 5 (10 amu) = 10.8

Isotopes We indicate isotopes by writing the mass alongside the element Boron – 11, Boron – 10 Carbon – 12, Carbon – 13, Carbon – 14

Isotopes and Radioactivity Radioactive means that an atom is emitting a particle As these atoms emit particles the element or isotope will change will change

Radioactive Isotopes Radioactive atoms have half-lives We can use radioactive isotopes to determine the age of things Radioactive atoms have half-lives Half-life – the amount of time it takes half the mass of the atoms to decay Carbon – 14 decays to Nitrogen – 14 1 half-life = 5,730 years A bone is discovered which has 25 percent of the carbon-14 found in the bones of other living animals. How old is the bone?

Chemical Bonds C, O, Cl, H, N, Na We’ve learned a few chemical symbols C, O, Cl, H, N, Na What about things like water and salt?

Compounds Ex. H2O, NaCl, SiO2 Chemical Compound – atoms that are chemically combined in a specific ratio Ex. H2O, NaCl, SiO2

Salt = Sodium and Chloride (NaCl) Compounds When compounds are formed, the elements take on new properties Sodium (Na) is a soft but reactant metal Chlorine (Cl) is a yellow-green toxic gas But combined…they make SALT! Salt = Sodium and Chloride (NaCl) + =

Compounds Why do atoms form compounds? Stability! Atoms will combine if they are more stable together than apart Atoms want to have 8 valence electrons to be “happy” (or 2 in He)

Noble Gases If we look at a Lewis dot diagram of the noble gases we can see they have a complete outer energy level (shell)

Hydrogen and Helium Hydrogen and helium are found in period 1 of the periodic table He contains 2 electrons in its first and only shell and it is stable H contains only 1 electron so it is not stable H is more stable when part of a compound This is why H is commonly found as part of so many chemical compounds

Chemical Bonds So how do elements fill their outer shell? They must gain or lose an electron! Elements that do not have a full outer shell will need to add or lose electrons to reach a stable level Metals usually give up an electron Nonmetals will usually take an electron

Ions If an atom gains or loses electrons it becomes an ion Ion – a charged atom due to the gain or loss of electrons

The Ionic Bond Ionic Bond – force of attraction between oppositely charged ions Positive (+) and negative (-) ions are attracted to each other like magnets! The result of this bond is a neutral compound! The charges cancel each other out

The Ionic Bond What if there is more than 1 electron involved?! In NaCl Na has 1 valance electron Cl has 8 valance electrons 1 atom of Na can form an ionic bond with 1 atom of Cl What if there is more than 1 electron involved?!

The Ionic Bond How would Mg and Cl form an ionic bond?

The Ionic Bond Not all molecules involve only 2 atoms! Mg and Cl bond to form MgCl2

The Ionic Bond The result of an ionic bond is a neutral compound The sum of the charges on the ions is ZERO Usually occur between a metal and a nonmetal Electrons are TAKEN by the atom with a stronger pull!

Electronegativity

The Covalent Bonds Some atoms of nonmetals are less likely to gain or lose electrons Take a look at C in group 4 Gain 4 electrons or lose 4 electrons to have a stable 8! That’d take a lot of energy!

The Covalent Bond Each time an atom loses and electron, the remain electrons are pulled in tighter It is more stable for these atoms to SHARE electrons! Covalent bond – bond formed between atoms when electrons are shared

Single and Multiple Bonds Single Bond 2 electrons (1 pair) are shared Usually 1 electron from one atom and 1 from the other Multiple Bonds Bonds containing more than 1 pair of electrons Double and triple N2

Ionic vs. Covalent Ionic Bonds Covalent Bonds Electrons taken Electrons shared

Unequal Sharing Electrons aren’t always shared equally in a covalent bond Electronegativity – the amount of attraction an atom has for its electrons This causes electrons to be pulled to one side of a molecule

Electronegativity

Polar or Nonpolar Due to unequal sharing, molecules can have slight charges! Electrons are pulled toward one side causing a slight negative charge Can only happen with uneven molecules

Polar vs. Nonpolar Polar Molecules Nonpolar Molecules Molecule with slight positive and negative ends Still neutral charge overall Nonpolar Molecules Electrons are equally shared across the molecule Do not have charges ends

Water Water is considered by many to be the “universal solvent” Water is a polar molecule Try to draw one molecule of water from memory…

Water

Hydrogen bonding When a H (a very small atom) is bonded to a larger more electronegative atom hydrogen bonding can occur Hydrogen bond – the strong force of attraction between two polar molecules containing a hydrogen atom. Holds heat Great solvent Ice floats

Chemical Reactions Everything to the left of the arrow are called the reactants Everything found on the right of the arrow are the products In chemistry we say the arrow “yields” the reactants

Chemical Reactions Remember, energy cannot be created nor destroyed? Neither can matter! (elements!) Within any chemical reaction, the equation must be balanced

Balanced Reactions Sometimes in order to keep a reaction balanced we need to indicate the number of molecules by placing a number in from of it

Chemical Reactions H2 + O2 2H2O How about the reaction of hydrogen and oxygen to form water? HINT: Hydrogen and oxygen are both gases and are found in pairs H2 and O2 H2 + O2 2H2O

The Mole A mole is a certain number of items Mole = 6.02 x 1023 Dozen = 12 Baker’s dozen = 13 Million = 1,000,000 Mole = 6.02 x 1023

Oxidation States The numbers with positive and negative signs found on the periodic table are oxidation numbers The oxidation number is the most common number of electrons that must be transferred to meet the octet rule of 8 valence electrons + is given away - is taken

Oxidation States Occasionally elements may have more than one oxidation state Elements with multiple oxidation states will be indicated by a romon numeral Copper (I) 1+ Copper (II) 2+ Iron (II) 2+ Iron (III) 3+