Scientific Measurements
Ratio that equals 1; used to convert one unit to another
What is a conversion factor?
Intensive or extensive property? Boiling point of ethanol
Intensive
Remember: Extensive is only related to mass and volume
This subatomic particle has a negative charge
What is an electron?
True or False? Every element is defined by its mass number
False: Every element is defined by its ATOMIC NUMBER (aka number of protons !!!)
An atom has 14 protons and 16 neutrons. What is its mass number? Identify the element.
14 p, 16 n → A = 30 → Silicon (Si)
A lab balance shows 0.045 kg. Convert this mass to grams.
1 kilogram (kg) = 1000 grams (g)
45 g
Shape: Takes the shape of the container
Volume: Definite
Particles: Close together but can slide past each other
What is a liquid?
The small, dense center of an atom where protons and neutrons are found
What is the nucleus?
Atoms of the same element with different numbers of neutrons
What are isotopes?
An atom has a mass number of 80 and 35 protons. How many neutrons does it have? Identify the element.
A = 80, Z = 35 → N = 45 → Bromine (Br)
A piece of wire is 1.6 meters long. Express its length in millimeters.
1 meter (m) = 1000 millimeters (mm)
1600 mm
A car battery contains 2500 g of sulfuric acid (H₂SO₄). If the density of sulfuric acid is 1.84 g/mL, what is the volume of the acid in liters?
1.36 L
The number of these particles determines the element’s identity
What are protons?
This number represents the number of protons in the nucleus of an atom and identifies the element.
What is atomic number?
Write the isotope notation for an atom with 53 protons and 74 neutrons.
I-127
Convert 6.5 kilometers to centimeters.
1 meter (m) = 100 centimeters (cm)
1 kilometer (km) = 1000 meters (m)
650,000 cm
The change from a gas directly into a solid.
What is deposition?
Accounts for most of the atom’s volume
Electron Cloud
The total number of protons and neutrons in an atom
What is mass number?
Gallium has two isotopes:
Ga-69: 68.93 amu, 60.11%
Ga-71: 70.92 amu, 39.89%
Find the average atomic mass.
69.72 amu
Convert 1.5 weeks to seconds.
907,200 seconds
Identify if samples A, B and C are the same compound or different compounds according to the Law of Constant Composition. Find the mass ratio N:H.
Conversion Factor: 1 kilogram (kg) = 1000 grams (g)
Sample A: 3.0 g H, 14.0 g N
Sample B: 0.006 kg H, 0.028 kg N
Sample C: 1.0 g H, 14.0 g N
Sample A: 14.0/3.0 = 4.67g
Sample B: 28.0/6.0 = 4.67g
Sample C: 14.0/1.0 = 14.0g
A and B have the same mass ratio → same compound
C has a different mass ratio → different compound
The number of electrons in a neutral atom equals this.
What are protons?
The average mass of all isotopes of an element, measured in atomic mass units (amu)
What is average atomic mass?
A certain isotope has twice as many neutrons as protons and a mass number of 150. How many protons and neutrons does it have?
Let protons = p, neutrons = 2p
Mass number = p + 2p = 3p
3p = 150 → p = 50 protons → 100 neutrons