Transcript Atoms, Elements, and Ions

The Atom
An atom consists of a
• nucleus
–(of protons and neutrons)
• electrons in space about the nucleus.
Electron cloud
Nucleus
• An atom is the smallest particle of an
element that has the chemical
properties of the element.
• The atom is extremely small. One teaspoon
of water has 3 times as many atoms as the
Atlantic Ocean has teaspoons of water.
• If a large sports stadium were an atom, a
marble would represent the nucleus.
ATOMIC COMPOSITION
• Protons (p+)
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic mass units (amu)
but we can round to 1 for mass.
• Electrons (e-)
–
negative electrical charge
– relative mass = 0.0005 amu
but we can round to 0 for mass.
• Neutrons (no)
no electrical charge
– mass = 1.009 amu but we can round to 1 for
mass.
–
Atomic Number, Z
All atoms of the same element
have the same number of
protons in the nucleus, Z
13
Al
26.981
Atomic number
Atom symbol
AVERAGE Atomic Mass
Mass Number, A
• C-12, atom with 6 protons and 6 neutrons is
the mass standard
• = 12 atomic mass units (amu)
• Mass Number (A)
= # protons + # neutrons
• NOT on the periodic table
Isotopes
• Atoms of the same element (same Z)
but different mass number (A).
• Boron-10 (10B) has 5 p and 5 n
• Boron-11 (11B) has 5 p and 6 n
11B
10B
Figure 3.10: Two isotopes of
sodium.
Atomic Symbols
 Hyphen notation/mass notation - show the name of
the element, a hyphen, and the mass number in
sodium-23
 Nuclear symbol - show the mass number and atomic
number in
mass number
23 Na
atomic number
11
Isotopes?
Which of the following represent
isotopes of the same element?
Which element?
234
92
X
234
93
X
235
92
X
238
92
X
1. An __
___ is the smallest particle of
an element that has the chemical properties
of the element.
2. The 3 pieces of the atom are ________,
_________, and _________.
3. Atoms with the same number of protons
and electrons, but a different number of
neutrons are called ____________.
4. ___________ was an English scientist
who developed an atomic theory in the
early 1800s.