Atoms, Molecules and Compounds PDF

# Atoms, Molecules and Compounds ## Definitions - **Atoms:** A single element. - **Molecules:** 2 or more atoms of the same type bonded together. - **Compounds:** 2 or more atoms of different types bonded together. ## Why do atoms bond together? - Atoms bond to become stable - this means they h...

# Atoms, Molecules and Compounds ## Definitions - **Atoms:** A single element. - **Molecules:** 2 or more atoms of the same type bonded together. - **Compounds:** 2 or more atoms of different types bonded together. ## Why do atoms bond together? - Atoms bond to become stable - this means they have a *full set of electrons*. ## Types of Bonding - **Ionic bonding:** electrons are *lost* from one atom and *gained by* another. - **Covalent bonding:** electrons are *shared*. ## How do atoms make ionic bonds? - **Ionic bonding** occurs between *metals* and *nonmetals*. - The *outermost electrons* are called *valence electrons*. - All elements need to have a *complete outer shell of electrons*. - In ionic bonding, *metals* *lose* valence electrons to become stable and become *positively charged*. - *Nonmetals* *gain* valence electrons to become stable and become *negatively charged*. - *Opposite* charges *attract*. - We often refer to atoms as having an *octet* and being stable. ### How many electrons does oxygen need to gain to fill its orbital? - Oxygen will *gain 2e-*. - Because electrons are negative and it *gained 2*, oxygen now has a 2- charge. This is written as *O2-*.