atomic structure
DESCRIPTION
ATOMIC STRUCTURE. ESSENTIAL QUESTION…. How can you identify an element and/or isotope based on its subatomic particles?. COMPOSED OF THREE SUBATOMIC PARTICLES: PROTON ( POSITIVELY CHARGED) NEUTRON ( NO CHARGE ) ELECTRON ( NEGATIVELY CHARGED). What is an atom composed of?. - PowerPoint PPT PresentationTRANSCRIPT
ATOMIC STRUCTURE
ESSENTIAL QUESTION…..
How can you identify an element and/or isotope based on its subatomic particles?
• COMPOSED OF THREE SUBATOMIC PARTICLES:
– PROTON (POSITIVELY CHARGED)
– NEUTRON (NO CHARGE)
– ELECTRON (NEGATIVELY CHARGED)
WHAT IS AN ATOM COMPOSED OF?
BOTH IN THE NUCLEUS
ALL FOUND OUTSIDE THE NUCLEUS (ELECTRON CLOUD)
• PROTONS (p+)– Proton is nearly 2000 times more massive than the electron, but
equal in charge and opposite in sign to the electron– Number of protons in the nucleus is electrically balanced by an equal
number of electrons
• NEUTRONS (n0)– Mass almost exactly equal to that of the proton
• ELECTRONS (e-)– Mass of electron much less than the mass of a proton and
neutron– Equal number of protons and electrons = NEUTRAL ATOM
ABOUT THE PARTICLES…..
Properties of Subatomic Particles
Particle Symbol Location Charge Relative mass
Actual mass (g)
Electron e- Around nucleus 1–
1 1840
9.11×10-28
Proton p+ Nucleus 1+ 1 1.673×10-24
Neutron n0 nucleus 0 1 1.675×10-24
• REPRESENTS THE NUMBER OF PROTONS IN AN ATOM
• ELEMENTS ARRANGED BY INCREASING ATOMIC NUMBER
• UNIQUE TO A GIVEN ELEMENT• SINCE ALL ATOMS ARE
NEUTRAL, ATOMIC NUMBER ALSO TELLS US THE NUMBER OF ELECTRONS IN AN ATOM
• USUALLY FOUND AT THE TOP OF THE ELEMENT’S SYMBOL
ATOMIC NUMBER
11Na22.990Sodium
LecturePLUS Timberlake 7
LEARNING CHECK 1State the number of protons for atoms of each of the following:A. Nitrogen (N)1) 5 protons 2) 7 protons 3) 14 protonsB. Sulfur (S)1) 32 protons 2) 16 protons 3) 6 protons
C. Barium (Ba)1) 137 protons 2) 81 protons 3) 56 protons
• THE TOTAL NUMBER OF PROTONS AND NEUTRONS IN THE NUCLEUS OF AN ATOM
• MASS NUMBER – ATOMIC NUMBER = # NEUTRONS
• ROUND THIS NUMBER TO THE NEXT WHOLE NUMBER TO DETERMINE THE MASS NUMBER
MASS NUMBER
11Na22.990Sodium
Example: Sodium (Na)
Mass Number = 23Atomic Number = 11
______ 12
neutrons
-
PRACTICE FROM THE PERIODIC TABLE
Complete the following chart:
Name Symbol Mass Number
# protons
# neutrons
# electrons
Lithium
Mg
26
16
• DALTON THOUGHT THAT…..– Atoms could not be divided(indivisible)
….atoms can be divided– All atoms of an element are
IDENTICAL….not really!!– Atoms of an element have same
number of p+ and e-, but the number of n0 may be different
ISOTOPES
• ISOTOPES ARE…–Atoms of the same element with
the same number of protons, but different numbers of neutrons.
–Atoms of the same element (same atomic number) with different mass numbers
ISOTOPES
THE ISOTOPES OF HYDROGEN
All atoms have the same number of protons (p+=1)…….
….but different number of neutrons in the nucleus (which means these isotopes will have different mass numbers!!)
A
Z XA = mass number
(the total number of protons + neutrons)Z = atomic number
(the total number of protons)X = element symbol
ISOTOPIC NOTATION
READING ISOTOPIC NOTATION 46
21 Sc46 = mass number (the total number of protons (21) + neutrons
(25))21 = atomic number (the total number of protons (21))Sc = element symbol
(In a neutral atom, the number of electrons (21) is equal to the number of protons)
ANOTHER WAY OF WRITING AN ISOTOPE
46
21 Sc or Scandium-46
Name of the element followed by the mass number(This format does not include the atomic number)
LecturePLUS Timberlake 16
PRACTICE
16 31 65 O P Zn 8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n8 e- 15 e- 30 e-
LecturePLUS Timberlake 17
PRACTICEAn atom has 14 protons and 20 neutrons.
A. Its atomic number is1) 14 2) 16
3) 34B. Its mass number is
1) 14 2) 163) 34C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is1) 34X 2) 34X 3) 36X
16 14 14
• Most elements found as a mixture of isotopes
• Relative abundance of each isotope is constant
• Example: Potassium in bananas–93.25% of K atoms have 20 n0
–6.7302% of K atoms have 22 n0
–0.0117% of K atoms have 21 n0
LecturePLUS Timberlake 18
ISOTOPES
• Isotopes of an element differ in mass
• The more neutrons in an isotope, the greater the mass
• Still, isotopes of an element have the same chemical behavior
• Why? Chemical behavior depends on the number of e-, not n0 or p+
LecturePLUS Timberlake 19
ISOTOPES
LecturePLUS Timberlake 20
CALCULATING ATOMIC MASS
Percent abundance of isotopesMass of each isotope of that
elementAverage Atomic Mass= mass isotope1(percent abundance1) + mass isotope2(percent
abundance2) + …
100 100
LecturePLUS Timberlake 21
ATOMIC MASS OF MAGNESIUM
Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70%25Mg = 25.0 amu 10.13%
26Mg = 26.0 amu 11.17%Average atomic mass of Mg = 24.3 amu
Mg24.3
LecturePLUS Timberlake 22
LEARNING CHECK AT7
Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?
LecturePLUS Timberlake 23
SOLUTION AT7
Ga-69 (%/100)68.9 amu x 60.2 = 41.5 amu
for Gallium-69 100Ga-71 (%/100)70.9 amu x 39.8 = 28.2 amu
for Gallium-71 100
Atomic mass Ga = 69.7 amu