4.2 The Structure of an Atom
Properties of Subatomic Particles
Protons:
• Amount of positive charge varies among elements
• Proton: ___________ charged, found in _________
 charge: 1+
 nucleus must contain at least one
4.2 The Structure of an Atom
Properties of Subatomic Particles
Electrons
• Detected by ____________
• Electron: __________ charged, found _______ nucleus
 charge: 1
4.2 The Structure of an Atom
Properties of Subatomic Particles
Neutrons:
• 1932, James _______________
• Concluded:
– Neutral because a charged object didn’t cause ________________
• Neutron: ____________particle, found in ____________
– Mass almost exactly equal to a ____________’s
4.2 The Structure of an Atom
Comparing Subatomic Particles
• How particles behave
• No instrument shows the inside of an atom
• Using Mass, Charge, and Location
4.2 The Structure of an Atom
Atomic Number and Mass Number
Atomic Number:
• Number of ___________ in an atom of that element
– All atoms an element have the same atomic number
– Each element has a unique atomic number
• Atoms are ______________
 Atomic number also equals the number of _______ in an
atom of that element.
4.2 The Structure of an Atom
Atomic Number and Mass Number
Examples:
• A The atomic number of sulfur (S) is 16.
• B The atomic number of iron (Fe) is 26.
• C The atomic number of silver (Ag) is 47.
4.2 The Structure of an Atom
Atomic Number and Mass Number
Mass Number
•________ of the protons and neutrons
– To find the number of neutrons, you need:
• mass number
• atomic number
4.2 The Structure of an Atom
Isotopes
•Atoms of the same element that have
– different numbers of _________________
– different __________ numbers
• Named by _____________ numbers
• Example:
– oxygen has 3 isotopes: oxygen-16, oxygen-17, oxygen-18
– all three can react with hydrogen to form water or with iron
to form rust
4.2 The Structure of an Atom
Isotopes
• Hydrogen isotopes are an exception:
 noticeably different __________________
o Hydrogen-1 (Almost all hydrogen), Hydrogen-2, Hydrogen-3
o Hydrogen-1 has one proton, so adding a neutron doubles its mass
o ____________________: contains hydrogen-2 in place of hydrogen-1