compounds and molecules
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Compounds and Molecules. When two elements combine chemically it is called a compound. What is a compound?. How do you know how much of an element is in a compound?. - PowerPoint PPT PresentationTRANSCRIPT
Compounds and Molecules
When two elements combine chemically it is called a compound.
The number after the symbol in a compound tells the number of those elements in the compound. H2O – two hydrogen and one oxygen – 2:1
Elements combine with the same or different elements in order to fill their outer-most shell(orbit).
Elements in the 18th column have all their orbits full. They are the noble gasses and rarely combine with other elements.
What is a compound?
How do you know how much of an element is in a compound?
Why do elements combine?
What is special about noble gasses?
Chemical Bonds
When elements share electrons to make a compound, it is called a covalent bond.
When one element “steals” electrons from another element to make a compound, it is called an ionic bond.
What is a covalent bond?
What kind of bond forms when an element “steals” electrons from another element?
What is a molecule?
When two or more elements combine forming covalent bonds they are called molecules.
The ionic charge tells how many electrons an element wants to “take”, “give away”, or “share”.
Transition metals are elements that do not fill out their orbits from the inside out. They fill them however they like, but they can not overfill an orbit.
What does the ionic charge tell you about an element?
What is a transition metal?
Chemical Reactions
A Synthesis reaction involves two separate things joining to form one compound.
4Fe + 3O2 2Fe2O3
A Replacement reaction takes place when elements switch or replace each other.
2AgCl + Pb PbCl2 + 2Ag
A Decomposition reaction is a breaking down of a more complex substance into two simpler substances.
H2CO3 CO2 + H2O
What is a synthesis reaction?
What is a replacement reaction?
What is a decomposition reaction?
Acids contain the element hydrogen, have a sour taste – HCl.
Bases contain the elements oxygen and hydrogen, have a bitter taste, and feel slippery – NaOH.
An indicator is something that changes color in the presence of an acid or base: Litmus and pH paper.
Blue litmus turns red in an acid. Red litmus turns blue in a base. pH paper has a color coded scale from 1-14, 1 being the strongest acid and 14 the strongest base.
Kinds of CompoundsWhat is an acid?
What compound has a bitter taste and is slippery?
How can you tell if a substance is an acid or a base?
What is an indicator?
A substance that is neither an acid nor a base is a neutral - 7 on pH scale.
When an acid and a base combine chemically salt and water forms.
The process of combining an acid and a base is called neutralization.
NaOH + HCl NaCl + H2O
sodium hydroxide+hydrochloric acid salt+water
When oxygen combines with another element it forms an oxide.
What is the pH of a neutral substance?
How do you make a salt?
What is it called when you add an acid to a base?
What is an oxide?
Chemical reactions that give off heat, or energy, are called exothermic reaction.
Chemical reactions that absorb energy are called endothermic reactions.
What is an exothermic reaction?
What are reactions that absorb energy called?