Warm Up

• How can all of earth’s material be broken down into elements?

• What elements do you think are the most abundant in the human body?

• Name at least one element that exist as a solid. A gas.

The elements

• The Greeks were the first to explain why chemical changes occur.

• They proposed that all matter was composed of four substances: fire, water, earth, and air.

• All material on earth can be broken down into 100 different elements.

• How can so few elements make up millions of known substances?

• Compounds are made by combining atoms of the various elements, just as words are constructed from the 26 letters of the alphabet.

• All of the materials in the universe can be chemically broken down into about 100 different elements.

Words Compounds

• Compounds are made by combining atoms of the elements just as words are constructed from the letters in the alphabet.

The Elements

A. Abundances of Elements• The elements in living

matter are very different from those in the earth’s crust.

• In the human body, oxygen, carbon, hydrogen and nitrogen are the most abundant elements.

A. Abundances of Elements

• Nine elements account for about 98% of the earth’s crust, oceans and atmosphere.

Elements in the UniverseElements in the Universe These are the ten most common elements in the Universe as These are the ten most common elements in the Universe as

measured in parts per million, by mass [Wiki]:measured in parts per million, by mass [Wiki]: Element Parts per million Element Parts per million Hydrogen 739,000 739,000 Helium 240,000 240,000 Oxygen 10,700 10,700 Carbon 4,600 4,600 Neon1,3401,340 Iron1,0901,090 Nitrogen950950

Silicon650650Magnesium580580Sulfur440All Others650440All Others650

Element can have several meanings

Element

Element

Element

Microscopic formSingle atom of thatelement

Macroscopic formSample of thatelement large enoughto weigh on a balance

Generic formWhen we say the human body contains the element sodium or lithium, we do not mean that free elemental sodium or lithium is present. Rather we mean that atoms of these elements are present in some form.

B. Names and Symbols for the B. Names and Symbols for the ElementsElements

Each element has a name and a symbol.Each element has a name and a symbol. The symbol usually consists of the first one or The symbol usually consists of the first one or

two letters of the element’s name.two letters of the element’s name.

Sometimes the symbol is taken from the Sometimes the symbol is taken from the element’s original Latin or Greek name.element’s original Latin or Greek name.

• Examples:Examples: Oxygen O Oxygen O Krypton Kr Krypton Kr

• Examples:Examples: gold Au aurum gold Au aurum lead Pb plumbum lead Pb plumbum

Element Song

• http://www.privatehand.com/flash/elements.html

• http://education.jlab.org/elementflashcards/index.html

Trace metals

• Trace metals are metals in extremely small quantities, almost at the molecular level, that reside in or are present in animal and plant cells and tissue. They are a necessary part of good nutrition, although they can be toxic if ingested excess quantites.

• Trace metals include iron, magnesium, zinc, copper, chromium, nickel, cobalt, vanadium, arsenic, molybdenum, and selenium

Compounds

– composed of 2 or more elements in a fixed ratio

– properties differ from those of individual elements

– EX: table salt (NaCl)

B. Formulas of Compounds

• A compound is represented by a chemical formula in which the number and kind of atoms present is shown by using the element symbols and subscripts.Example: the simple sugar, glucose

HOW SMALL IS AN ATOM?

• At sea level and at 32oC, one cubic centimeter of air (that is, a space about the size of a sugar cube) will contain 45 billion billion molecules.

• Image a line -. Now divide that into 10,000 equal widths. Each width is a micron. Take a micron and divide it a million times. That’s the size of an atom.

Atoms Get Around• Every atom you possess has almost certainly

passed through several stars and been a part of millions of organisms on its way to becoming you.

• We are each so atomically numerous and so vigorously recycled at our death that a significant number of our atoms probably belonged to Shakespeare.

• Half a million atoms are lined up shoulder to shoulder could hide behind a human hair

1818thth Century Thoughts Century Thoughts

1) Most natural 1) Most natural materials are mixtures materials are mixtures of pure substancesof pure substances

2) pure substances are 2) pure substances are either elements or a either elements or a combo of elements combo of elements called compoundscalled compounds

3) a given compound 3) a given compound always contain the always contain the same proportion of same proportion of elementselements

Early Models of the Atom

• By the late 1700s, experiments carried out by French chemists Proust, Priestley, and Lavoisier suggested that matter might be made of atoms after all.

• After very careful experiments with precise measurements, English school teacher John Dalton combined his own ideas with those of the French chemists and proposed the first atomic theory of matter based on experimental results in 1803.

Dalton’s Atomic TheoryDalton’s Atomic Theory1. matter is composed, 1. matter is composed, indivisibleindivisible particles particles

Atoms Can Be Divided, but only in a nuclear reactionAtoms Can Be Divided, but only in a nuclear reaction2. all atoms of a particular element are identical2. all atoms of a particular element are identical

Does Not Account for Isotopes (atoms of the same element but Does Not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)!a different mass due to a different number of neutrons)!

3. different elements have different atoms3. different elements have different atomsYES!YES!

4. atoms combine in certain 4. atoms combine in certain whole-numberwhole-number ratios ratiosYES! Called the Law of Definite ProportionsYES! Called the Law of Definite Proportions

5. In a chemical reaction, atoms are merely 5. In a chemical reaction, atoms are merely rearrangedrearranged to form to form new compounds; they are not created, destroyed, or changed new compounds; they are not created, destroyed, or changed into atoms of any other elements.into atoms of any other elements.Yes, except for nuclear reactions that can change atoms of one Yes, except for nuclear reactions that can change atoms of one element to a different elementelement to a different element

Dalton’s ImpactDalton’s Impact People didn’t really believe People didn’t really believe

Dalton’s theory. Scientists Dalton’s theory. Scientists wanted better proofwanted better proof

For a century after Dalton For a century after Dalton made his proposal, it made his proposal, it remained hypothetical. remained hypothetical. Many scientists doubted Many scientists doubted the existence of atoms at the existence of atoms at all.all.

It was Einstein who It was Einstein who observed Brownian motion observed Brownian motion in 1905 thus proved atoms in 1905 thus proved atoms existedexisted

Law of Constant Composition

• A given compound always contains the same proportion by mass of the elements of which it is composed.

• The law of constant composition states that the composition of a substance is always the same, regardless of how the substance was made or where the substance is found.

• So, whenever we talk about water, we know that there are 2 atoms of hydrogen and 1 atom of oxygen in a molecule of water.

• As soon as the composition of a molecule changes, then you have a different substance with different properties.

Hennig Brand

• Wanted to fine the “philospher’s stone” which turned bass metals into gold.

• Around 1669 he heated residues from boiled-down urine on his furnace until the retort was red hot, where all of a sudden glowing fumes filled it and liquid dripped out, bursting into flames.

• He could catch the liquid in a jar and cover it, where it solidified and continued to give off a pale-green glow.

• What he collected was phosphorus, which he named from the Greek for "light-bearing" or "light-bearer."

Carl Schelee (1742-1786)

Devised a way to manufacture phosphorus without urine.

Hense why Sweden is still #1 in matches.

Discovered Oxygen, chlorine, fluorine, nitrogen and got no credit for it!!

Loved Tasting Chemicals… Mercury, hydrocyanic acid

Died at 43 surrounded by toxic chemicals and had a stunned look on his face

J.J Thompson

• Late 1890’s, Mr. Thompson used a cathode ray tube to show that atoms of any element can be made to emit tiny negative particles.

• Discovered Electrons. But they must be balanced by positive particles.

A. The Structure of the Atom

The Plum Pudding Model

Ernest Rutherford

• From New Zealand and got a scholarship to Cambridge and worked under Thompson.

• In 1910, Rutherford fired ionized helium atoms, or alpha particles, at a sheet of gold foil.

• To Rutherford’s astonishment, some of the particles bounced back.

• It was if, he said, he had fired a fifteen inch shell at a sheet of paper and it rebounded on his lap.

• Explanation: The particles that bounced back were striking something small and dense at the heart of the atom.

Rutherford

Rutherford’s Experiment

Rutherford

Discovery of the Neutron

• In 1935, James Chadwick received the Nobel Prize in Physics for finding neutrons.

• When Rutherford discovered the proton, he figured that there must be another particle making up the mass of the nucleus. The Curies (of radiation fame) also worked to find the neutron but misread their results and missed the discovery. (they won the Nobel Prize in Chemistry in 1935 so don’t feel so bad.)

Introduction to the Modern Concept of Atomic Structure

• Ernest Rutherford showed that atoms have internal structure.– The nucleus, which is at the

center of the atom, contains protons (positively charged) and neutrons (uncharged).

– Electrons move around the nucleus.

ATOM ATOM COMPOSITIONCOMPOSITION

•protons and neutrons in protons and neutrons in the nucleus.the nucleus.

•the number of electrons is equal to the the number of electrons is equal to the number of protons.number of protons.

•electrons in space around the nucleus.electrons in space around the nucleus.

•extremely small. One teaspoon of water has extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean 3 times as many atoms as the Atlantic Ocean has teaspoons of water.has teaspoons of water.

The atom is mostlyThe atom is mostlyempty spaceempty space

ATOMIC COMPOSITIONATOMIC COMPOSITION Protons (pProtons (p++))

+ electrical charge+ electrical charge mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g relative mass = 1.007 atomic relative mass = 1.007 atomic mass mass

units (amu) units (amu) but we can round to 1but we can round to 1 Electrons (eElectrons (e--))

negative electrical chargenegative electrical charge relative mass = 0.0005 amu relative mass = 0.0005 amu

but we can round to 0but we can round to 0 Neutrons (nNeutrons (noo))

no electrical chargeno electrical charge mass = 1.009 amu mass = 1.009 amu but we can round to 1but we can round to 1

If all atoms are composed of these same components, why do different atoms have different properties The answer lies in the number and

arrangement of the electrons. The electrons are the parts of atoms that

“intermingle” when atoms combine to form molecules.

As a result, atoms of different elements, which have different numbers of electrons, show different chemical behavior.

Atomic Number, ZAtomic Number, ZAll atoms of the same element have the All atoms of the same element have the

same number of protons in the same number of protons in the nucleusnucleus, , ZZ

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

AVERAGE Atomic MassAVERAGE Atomic Mass

Mass Number, AMass Number, A C atom with 6 protons and 6 neutrons is C atom with 6 protons and 6 neutrons is

the mass standard the mass standard = 12 atomic mass units= 12 atomic mass units Mass NumberMass Number (A) (A)

= # protons + # neutrons= # protons + # neutrons NOT on the periodic table…(it is the NOT on the periodic table…(it is the

AVERAGE atomic mass on the table)AVERAGE atomic mass on the table) A boron atom can have A boron atom can have

A = 5 p + 5 n = 10 amuA = 5 p + 5 n = 10 amu

A

Z

10

5B

A

Z

10

5B

IsotopesIsotopes

Atoms of the same element (same Z) Atoms of the same element (same Z) but different mass number (A).but different mass number (A).

Boron-10 (Boron-10 (1010B) has 5 p and 5 nB) has 5 p and 5 nBoron-11 (Boron-11 (1111B) has 5 p and 6 nB) has 5 p and 6 n

10B

11B

Figure 3.10: Two isotopes of sodium.

Isotopes & Isotopes & Their UsesTheir Uses

Bone scans with Bone scans with radioactive radioactive technetium-99. technetium-99.

Isotopes & Their UsesIsotopes & Their Uses

The The tritiumtritium content of ground water is content of ground water is used to discover the source of the water, used to discover the source of the water, for example, in municipal water or the for example, in municipal water or the source of the steam from a volcano. source of the steam from a volcano.

Atomic Symbols

Show the name of the element, a hyphen, and the mass number in hyphen notation

sodium-23

Show the mass number and atomic number in nuclear symbol formmass number 23 Na

atomic number 11

Isotopes?

Which of the following represent isotopes of the same element? Which element?

234 X 234

X235

X238

X

92 93 92 92

Counting Protons, Neutrons, and Electrons

Protons: Atomic Number (from periodic table)Neutrons: Mass Number minus the number of

protons (mass number is protons and neutrons because the mass of electrons is negligible)

Electrons: If it’s an atom, the protons and electrons must be the SAME

so that it is has a net charge of zero (equal numbers of + and -)

If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

Warm up 1/30/2013 – Counting

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p+ _______ _______ _______

#no _______ _______ _______

#e- _______ _______ _______

Answers

12C 13C 14C 6 6 6

#p+ 6 6 6

#no 6 7 8

#e- 6 6 6

Learning Check

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is

1) 34X 2) 34X 3) 36X 16 14 14