Atom is the smallest particle of an
element. Atoms cannot be divided
into anything smaller.
What is an atom made of?
• Three subatomic particles:–Proton–Neutron–electron
+ PROTONS +• Positively charged subatomic particle• Found in the nucleus of an atom–Center of the atom
• Each proton is assigned a charge of 1+. • Each nucleus must contain at least one
proton.• Mass is equal to the mass of a neutron
- ELECTRONS -• negatively charged subatomic
particle• found in the space outside the
nucleus. – Electron cloud
• Each electron has a charge of 1.• Mass is much smaller than the mass
of protons & neutrons.– 2000 electrons equal the mass of one proton
NEUTRONS• Neutral subatomic particle–Neither negative or positive
• Found in the nucleus of an atom. –Center of the atom.
• Mass almost exactly equal to that of a proton.
Atomic Number• Equals the number of protons and
electrons• Each element has a unique atomic
number.Atomic Number13
AlAluminum 29.982
Mass Number• The mass number of an atom is the sum of
the protons and neutrons in the nucleus of that atom.
13Al
Aluminum 29.982 Mass Number
…How do you find the number of neutrons?
13Al
Aluminum 26.982 Mass Number
Atomic NumberThe atomic number of aluminum is 13. An atom of aluminum that has a mass number of 27 has 13 protons and 14 neutrons.
Isotopes
What is an Isotope?
• Atoms with the same number of protons and electrons but different numbers of neutrons• Many elements have two or more
isotopes–Stable isotopes–Unstable isotopes
Isotopes
• Can distinguish one form another by looking at the mass number:– Each number represents the mass number• Oxygen has 3 isotopes: Oxygen-16, Oxygen-17, and
Oxygen-18• Carbon has 3 isotopes: Carbon-12, Carbon-13, and
Carbon-14
Stable Isotopes
• An element whose nucleus does not spontaneously give off particles or energy
• Of the known chemical elements, 80 elements have at least one stable nuclei. – These comprise the first 82 elements
from hydrogen to lead, with the two exceptions, technetium (element 43) and promethium (element 61), that do not have any stable nuclei.
• Tin has ten stable isotopes
Unstable Isotope• An element whose nucleus decomposes, or
decays, by losing particles and energy.
• Radioactive• The energy or particles that are emitted from the nucleus is called radiation• 3 Types of radiation: Alpha, Beta,
Gamma• Used to determine the age of fossils
Example of Isotopes• Carbon has three isotopes and they are
carbon 12, carbon 13 and carbon 14. – Carbon 12 & 13 are stable isotopes – Carbon 14 is an unstable isotope
Isotope NotationHow to write isotopes
• 1st-Element name-mass number– Examples• Oxygen has 3 isotopes: Oxygen-16, Oxygen-17, and
Oxygen-18 • Carbon has 3 isotopes: Carbon-12, Carbon-13, and
Carbon-14
• 2nd-
Calculating Isotopes• You will use the mass number and the atomic number
of the isotope to determine the number of neutrons in the nucleus.• Neutrons=Mass number-atomic number
• Example:– Oxygen has 3 isotopes:
• Oxygen-16• Oxygen-17 Each of these numbers represents the mass number
• Oxygen-18
– Oxygen’s atomic number=8– How many neutrons does each isotope of oxygen
have?
Calculating IsotopesHow many neutrons does each isotope below have?