Significant Figures
How many significant figures are in 0.0029?
2 significant figures
Even if there is a decimal point, all the zeroes BEFORE the 2 are NEVER significant.
Hydrogen gas
Element
Color
Physical property
Where do you find the number of protons of an element on the periodic table?
The atomic number, found in the corner of the box
The charge of an ion depends on both protons and electrons, but only the _______ can change
Electrons
To make an ion positive, you take away electrons so that there are fewer electrons than protons
To make an ion negative, you add electrons so that there are more electrons than protons
A neutral atom will have the same number of protons and electrons
How many significant figures are in 486000?
3 significant figures
Since there is no decimal point, all of the zeroes AFTER the 6 will NOT be significant.
Salt water
Homogenous mixture
Metal rusting
Chemical change
How many protons are in oxygen?
8 protons
The atomic number (on the periodic table) matches the element's number of protons
How many electrons are in Na+?
10 electrons
Since the charge is +1, it will have one fewer electron than its number of protons; it has 11 protons according to the periodic table
How many significant figures should your answer have when you ADD 0.45 + 1.096?
2 significant figures
When you add or subtract numbers, your answer should have the same number of sigfigs as the number with the least amount of digits AFTER THE DECIMAL. (Line it up vertically!)
Methane (CH4)
Compound
pH (acidity)
What is the mass number of this isotope?
12 C
6
12
The mass number is on top, and the atomic number (# of protons, same as on the periodic table) is on the bottom
How many protons are in Mg2+?
12 protons
The charge NEVER changes the number of protons, otherwise it would be a different element
How many significant figures are in 4.890 x 105?
4 significant figures
When you look at scientific notation, ignore the 105 and count the significant figures of the coefficient (4.890).
Sand on the beach
Homogenous mixture (sand, shells, rocks)
The sand itself is a compound
Density
Physical property
How many neutrons are in this isotope?
14 C
6
8 neutrons
Since there are 6 protons, you subtract these from the mass number of 14
What is the difference between a cation and an anion?
A cation is a positive ion
An anion is a negative ion (think: N-ion)
How many significant figures should your answer have when you MULTIPLY 3.37 x 2.8?
2 significant figures
When you multiply or divide numbers, your answer should have the same amount of sigfigs as the number with the least amount of TOTAL sigfigs.
Air
Homogenous mixture
Dissolving salt in water
Physical change
Which two subatomic particles are found in the nucleus of an atom?
Protons and neutrons
These make up the atomic mass in the center of the atom, while electrons are floating around them
How many electrons are in O2-?
10 electrons
Since oxygen has 8 protons, a -2 charge would mean that it has 2 more electrons than protons