Download Intro to atoms - Junior Cert Science

Atoms
Atoms
•
•
•
•
•
•
The smallest particle making up elements
Atoms consist of three types of particles
Neutrons with a neutral charge
Protons with a positive charge
Electrons with a negative charge
Mass is measured in a.m.u.
(atomic mass unit)
The positive (+) particle is called a
proton
+
1 a.m.u.
The neutral (no charge) particle is called a
Neutron
N
1 a.m.u.
The negative (–) particle is called an
electron
–
1 a.m.u.
1840
In an atom, protons + and neutrons N
are in the centre (nucleus) and electrons
– circle the nucleus in orbits or shells
–
–
–
+N+
N + +N
+N N
–
–
Bohr Model
Bohr model of an Atom
• Maximum of 2 electrons in First shell (n = 1)
• Maximum of 8 electrons in Second shell (n = 2)
• Maximum of 8 electrons in Third shell (n = 3)
–
–
–
6P
6N
–
–
–
Periodic Table
number of
protons and
electrons
6
Atomic
number
C
Symbol
12.011
Atomic Mass
(average)
atomic mass – atomic number = number of neutrons
Isotopes
 Atoms of the same element but
different mass number
 Boron-10 (10B) has 5 p and 5 n
 Boron-11 (11B) has 5 p and 6 n
11B
10B
Isotopes of sodium
Isotopes and their usage
Bone scans with
radioactive Technetium-99
The tritium 3H content of ground water is used
to discover the source of the water, for
example, in municipal water or the source
of the steam from a volcano.
Counting particles
• 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.
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.
12
C
6
13
C
6
14
C
6
6
#p+ _______
6
_______
6
_______
6
#no _______
6
#e- _______
7
_______
6
_______
8
_______
6
_______
Learning Check – Counting
An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) 14
2) 16
3) 34
B. Its mass number is
1) 14
2) 16
3) 34
C. The element is
1) Si
3) Se
2) Ca
D. Another isotope of this element is
34X
34X
36X
1) 16
2) 14
3) 14