Elements, Atoms, and

Ions

Chemistry I: Chapter 2b

Chemistry I Honors: Chapter 3

ICP: Chapter 17

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The Language of The Language of ChemistryChemistry

• CHEMICAL ELEMENTSCHEMICAL ELEMENTS - - – pure substances that cannot be decomposed by pure substances that cannot be decomposed by

ordinary means to other substances.ordinary means to other substances.

Sodium Bromine

Aluminum

The Language of The Language of ChemistryChemistry

• The elements, The elements, their names, and their names, and symbols are given symbols are given on theon the PERIODIC PERIODIC TABLETABLE

• How many How many elements are elements are there?there?

The Periodic TableThe Periodic Table

Dmitri Mendeleev (1834 - 1907)Dmitri Mendeleev (1834 - 1907)

Glenn Glenn SeaborgSeaborg

(1912-1999 )(1912-1999 )• Discovered 8 Discovered 8

new elements.new elements.• Only living Only living

person for person for whom an whom an element was element was named.named.

An atom consists of aAn atom consists of a • nucleusnucleus

– (of (of protonsprotons and and neutronsneutrons) ) • electronselectrons in space about the nucleus. in space about the nucleus.

The The AtomAtom

NucleusNucleus

Electron cloudElectron cloud

Copper Copper atoms on atoms on silica silica surface.surface.

• An An __________ is the smallest particle of is the smallest particle of an element that has the chemical an element that has the chemical properties of the element.properties of the element.

Distance across = 1.8 nanometer (1.8 x 10-9 m)

Subatomic ParticlesSubatomic Particles

• Quarks– component of component of

protons & protons & neutronsneutrons

– 6 types6 types

– 3 quarks = 3 quarks = 1 proton or 1 proton or 1 neutron1 neutron

He

The red compound is The red compound is composed ofcomposed of• • nickel (Ni) (silver)nickel (Ni) (silver)• • carbon (C) (black)carbon (C) (black)• hydrogen (H) (white)• hydrogen (H) (white) • • oxygen (O) (red)oxygen (O) (red)• • nitrogen (N) (blue)nitrogen (N) (blue)

CHEMICAL COMPOUNDSCHEMICAL COMPOUNDS are composed of atoms and so can are composed of atoms and so can be decomposed to those atoms.be decomposed to those atoms.

Compounds

– composed of 2 or more elements in a fixed ratio

– properties differ from those of individual elements

– EX: table salt (NaCl)

AA MOLECULEMOLECULE is the smallest unit of is the smallest unit of a compound that retains the chemical a compound that retains the chemical characteristics of the compound.characteristics of the compound.

Composition of molecules is given by aComposition of molecules is given by a MOLECULAR FORMULAMOLECULAR FORMULA

HH22OO CC88HH1010NN44OO22 - caffeine - caffeine

ELEMENTS THAT EXIST AS ELEMENTS THAT EXIST AS DIATOMICDIATOMIC MOLECULES MOLECULES

Remember:

BrINClHOFThese elements only exist as

PAIRS. Note that when they

combine to make compounds, they

are no longer elements so they are no longer in

pairs!

Dalton’s Atomic Theory

John Dalton (1766-1844) proposed an atomic theory

While this theory was not completely correct, it revolutionized how chemists looked at matter and brought about chemistry as we know it today instead of alchemy

Thus, it’s an important landmark in the history of science.

Dalton’s Atomic Theory - Summary

1. matter is composed, indivisible particles (atoms)2. all atoms of a particular element are identical3. different elements have different atoms4. atoms combine in certain whole-number ratios 5. In a chemical reaction, atoms are merely

rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.

Problems with Dalton’s Atomic Theory?1. matter is composed, indivisible particles

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

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

3. different elements have different atomsYES!

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

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

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 units (amu) mass 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

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

have the same number of have the same number of protons in the nucleus, protons in the nucleus, ZZ

1313AlAl

26.98126.981

Atomic numberAtomic numberAtom symbolAtom symbol

AVERAGE Atomic MassAVERAGE Atomic Mass

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

is the mass standard is 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 amuAZ

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 n• Boron-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 & Their

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

Isotopes & Their Isotopes & Their UsesUses

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!)

Learning Check – 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 is1) 142) 163) 34

B. Its mass number is1) 142) 163) 34

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

D. Another isotope of this element is1) 34X 2) 34X 3) 36X

16 14 14

IONS IONS • IONSIONS are atoms or groups of atoms with a positive or negative are atoms or groups of atoms with a positive or negative

charge. charge.

• Taking awayTaking away an electron from an atom gives a an electron from an atom gives a CATIONCATION with a with a positive chargepositive charge

• AddingAdding an electron to an atom gives an an electron to an atom gives an ANIONANION with a with a negative negative chargecharge..

• To tell the difference between an atom and an ion, look to see if there is To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Naa charge in the superscript! Examples: Na++ Ca Ca+2+2 I I-- O O-2-2

Na Ca I ONa Ca I O

Forming Cations & Forming Cations & AnionsAnions

A A CATIONCATION forms forms when an when an atom atom losesloses one or one or more electrons.more electrons.

An An ANIONANION forms forms when an when an atom atom gainsgains one or one or more electronsmore electrons

Mg --> Mg2+ + 2 e- F + e- --> F-

PREDICTING ION CHARGESPREDICTING ION CHARGES

In generalIn general

• metalsmetals (Mg) (Mg) lose electrons lose electrons ---> ---> cationscations

• nonmetalsnonmetals (F) (F) gain electronsgain electrons ---> ---> anionsanions

Learning Check – Counting

State the number of protons, neutrons, and electrons in each of these ions.

39 K+ 16O -2 41Ca +2

19 8 20

#p+ ______ ______ _______

#no ______ ______ _______

#e- ______ ______ _______

One Last Learning Check

Write the nuclear symbol form for the following atoms or ions:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 46 e- ___________

Charges on Common Charges on Common IonsIons

-1-2-3+1+2

By losing or gaining e-, atom has same By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.number of e-’s as nearest Group 8A atom.

AVERAGE AVERAGE ATOMIC ATOMIC MASSMASS

• Because of the existence of isotopes, the Because of the existence of isotopes, the mass of a collection of atoms has an average mass of a collection of atoms has an average value.value.

• Boron is 20% Boron is 20% 1010B and 80% B and 80% 1111B. That is, B. That is, 1111B is B is 80 percent abundant on earth. 80 percent abundant on earth.

• For boron atomic weightFor boron atomic weight = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

10B

11B

Isotopes & Average Atomic Isotopes & Average Atomic MassMass

• Because of the existence of isotopes, the mass Because of the existence of isotopes, the mass of a collection of atoms has an average value.of a collection of atoms has an average value.

• 66Li = 7.5% abundant and Li = 7.5% abundant and 77Li = 92.5%Li = 92.5%

–Avg. Atomic mass of Li = ______________Avg. Atomic mass of Li = ______________

• 2828Si = 92.23%, Si = 92.23%, 2929Si = 4.67%, Si = 4.67%, 3030Si = 3.10%Si = 3.10%

–Avg. Atomic mass of Si = ______________Avg. Atomic mass of Si = ______________

The Periodic Table

PeriodsPeriods in the Periodic in the Periodic TableTable

GroupsGroups in the Periodic in the Periodic TableTable

Elements in groups react in similar ways!

Regions of the Periodic Regions of the Periodic TableTable

Group 1A: Alkali MetalsGroup 1A: Alkali Metals

Cutting sodium metalCutting sodium metal

Reaction of potassium + H2O

MagnesiumMagnesium

Magnesium Magnesium oxideoxide

Group 2A: Alkaline Earth MetalsGroup 2A: Alkaline Earth Metals

Group 7A: The Halogens Group 7A: The Halogens (salt makers) (salt makers) F, Cl, Br, I, AtF, Cl, Br, I, At

Group 8A: The Noble Group 8A: The Noble (Inert) Gases(Inert) Gases

He, Ne, Ar, Kr, Xe, RnHe, Ne, Ar, Kr, Xe, Rn• Lighter than air

balloons• “Neon” signs• Very Unreactive

because they have full electron levels

XeOFXeOF44

Transition ElementsTransition Elements

Lanthanides and actinidesLanthanides and actinides

Iron in air gives Iron in air gives iron(III) oxideiron(III) oxide

Rutherford’s experiment.

The modern view of the atom was developed The modern view of the atom was developed by by Ernest RutherfordErnest Rutherford (1871-1937). (1871-1937).

Results of foil

experiment if Plum

Pudding model had

been correct.

What Actually Happened