Atoms & Elements
Atoms - smallest part of a pure substance/element
● The group number in the periodic table tells you the quantity of electrons in the outer
shell
● The proton/atomic number is equal to the number of electrons
Atomic number (Z) - The number of protons in the nucleus
Mass number (A) - The number of protons and neutrons in the nucleus
Ion - A positively or negatively charged atom/group of
atoms
Chlorine’s atomic mass is
Isotopes - Isotopes are atoms of the same element with 35.5 because some are
different numbers of neutrons but the same number of 35 and some are 37.
protons and electrons They are Isotopes
● Isotopes have almost identical properties
● There are some differences
○ E.g boiling points
● Mixing these hydrogen isotopes creates heavy water
● When an ion is positive it has lost electrons
● When an ion is negative it has gained electrons
The Aufbau principle
● Electrons start filling up from the innermost shell
● Shell one can carry two electrons
● Shells two and three can carry eight electrons
● Shell four can carry ten
Atoms - smallest part of a pure substance/element
● The group number in the periodic table tells you the quantity of electrons in the outer
shell
● The proton/atomic number is equal to the number of electrons
Atomic number (Z) - The number of protons in the nucleus
Mass number (A) - The number of protons and neutrons in the nucleus
Ion - A positively or negatively charged atom/group of
atoms
Chlorine’s atomic mass is
Isotopes - Isotopes are atoms of the same element with 35.5 because some are
different numbers of neutrons but the same number of 35 and some are 37.
protons and electrons They are Isotopes
● Isotopes have almost identical properties
● There are some differences
○ E.g boiling points
● Mixing these hydrogen isotopes creates heavy water
● When an ion is positive it has lost electrons
● When an ion is negative it has gained electrons
The Aufbau principle
● Electrons start filling up from the innermost shell
● Shell one can carry two electrons
● Shells two and three can carry eight electrons
● Shell four can carry ten
