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Elements, Atoms, and Compounds
The Language of The Language of ChemistryChemistryThe 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.
SodiumBromine
Aluminum
The Language of The Language of ChemistryChemistryThe 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)
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)
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
– 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
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 mass units (amu) (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, Z
All 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
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 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 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 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 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
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