Elements and Compounds
what is the smallest unit of an element that still retains its properties?
Atom
what does the atomic number represent?
# of protons
State the Law of Conservation of Mass.
mass cannot be created or destroyed in a chemical reaction
State the Law of Definite Proportions.
A compound always has the same composition by mass.
State the Law of Multiple Proportions.
If 2 elements form multiple compounds, the ratios of their masses are small whole numbers.
Is Oxygen an element or a compound?
Element
Which group is the noble gases?
group 18
20g hydrogen reacts with 160g oxygen. How much water forms?
180g
In H2O, what is the ratio of hydrogen to oxygen atoms?
2:1
Carbon forms CO and CO2. What Law explains this?
Law of Multiple Proportions
Which is a compound: Na; H2O; Cl2; Fe?
H2O
Name 1 metalloid.
Boron, Silicon, Arsenic, Tellurium, Antimony
If a reaction starts with 50g reactants, how many grams of product form?
50g
If CO2 contains 27.3% carbon by mass, what % is oxygen?
72.7%
12g Carbon + 16g Oxygen = CO. How many grams of oxygen combine with 12g carbon to form CO2?
32g Oxygen
Why is water a pure substance even though it contains 2 elements?
chemically combined in fixed ratio
How many valence electrons does chlorine have?
7
True or False. Mass can be created in a chemical reaction?
False. It is only rearranged.
True or False. What in Louisiana has a different composition than water in Texas.
False. always H2O
Give another example of an element that forms more than one compound.
Nitrogen+Oxygen; Iron+Oxygen
Compare and contrast mixtures and compounds?
Mixtures are physically combinded; compounds are chemically combined in fixed ratios.
Why are elements in the same group similar in chemical properties?
same number of valence electrons
Why is a closed system necessary to prove the law of conservation of mass?
Prevents gas/products from escaping
Why does NaCl always have the same composition by mass?
Sodium and Chlorine bond in a fixed 1:1 ratio
Why was the Law of Multiple Proportions important in developing atomic theory?
Supported Dalton's atomic theory with evidence of atoms combining in simple ratios.