All atoms of an element have the same number of protons and the same atomic number Learning Goal Given the atomic number and the mass number of an atom state the number of protons neutrons and electrons ID: 633814
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Slide1
4.4 Atomic Number and Mass Number
All atoms of an element have the same number of protons and the same atomic number.
Learning Goal Given the atomic number and the mass number of an atom, state the number of protons, neutrons, and electrons.Slide2
Atomic Number
The
atomic number is a whole number specific for each element. is the same for all atoms of an element.is equal to the number of protons in an atom.appears above the symbol of an element in the periodic table.11Na
Atomic number
SymbolSlide3
Atomic Number = Protons in an Atom
Atomic number = number of protons—for example,
the atomic number of H is 1; every H atom has one proton.the atomic number of C is 6; every C atom has six protons.the atomic number of Cu is 29; every Cu atom has 29 protons.Core Chemistry Skill Counting Protons and NeutronsSlide4
Atomic Number = Protons in an Atom
All atoms of lithium
(left) contain three protons, and all atoms of carbon (right) contain six protons. Slide5
Atoms are Neutral
For neutral atoms, the net charge is
zero. number of protons = number of electronsAluminum has 13 protons and 13 electrons. The net (overall)charge is zero. 13 protons (13+) + 13 electrons (13–) = 0Slide6
Study Check
Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements:
ElementAtomic NumberProtons
Electrons
N
Zn
SSlide7
Solution
Use the periodic table to fill in the atomic
number, number of protons, and number of electrons for each of the following elements:
Element
Atomic
Number
Protons
Electrons
N
7
7
7
Zn
30
30
30
S
16
16
16Slide8
Mass Number
The mass number
represents the number of particles in the nucleus.is equal to the number of protons + the number of neutrons.is always a whole number.does not appear in the periodic table.Slide9
Composition of Some Atoms of Different ElementsSlide10
Study Tips: Protons and Neutrons
Number of
protons = atomic numberNumber of protons + neutrons = mass numberNumber of neutrons = mass number – atomic numberNote: Mass numbers are given for specific isotopes only.Slide11
Study Check
An atom of lead (Pb
) has a mass number of 207. A. How many protons are in the nucleus?B. How many neutrons are in the nucleus?C. How many electrons are in the atom?Slide12
Solution
An atom of lead (Pb) has a mass number of 207.
A. How many protons are in the nucleus? atomic number = 82; number protons = 82B. How many neutrons are in the nucleus? mass number – number protons = number neutrons 207 – 82 = 125 neutronsC. How many electrons are in the atom? An atom is neutral, which means that the number of electrons is equal to the number of protons. An atom of Pb has 82 protons and 82 electrons.