BL Ch 2 Atoms, Molecules and Ions PPt

Multiple Choice

Why is the study of atoms, molecules, and ions significant in understanding the nature of matter?

• Because they are the fundamental building blocks of all substances

• Because they are only found in living organisms

• Because they are only important in physics

• Because they do not interact with each other

​This does not mean that the number of substances can not change, they probably will as will their properties, but the total amount of matter must remain constant. H2 + O2 --> H2O

​Law of Definite Proportion - no matter its source, a particular compound is composed of the same element in the same part (fraction) by mass.

Example: NaCl (salt) contain 1 sodium atom with a mass of 22.900 g and
1 chlorine atom with a mass of 35.453 g
Therefore, the fraction (or Percent each is of the compound remains the same.
In this case, the total mass of NaCl is 22.900 + 35.453 = 58.353 g
The percent by mass of Na = 22.900/58.353 or 39.2%
The percent by mass of Cl = 35.453/58.353 or 60.8%

If you have a 20 g sample of salt then it would contain 20g (.392) = 7.84 g of Na and 20g (.608) = 12.16 g of Cl

​Example 1: H₂O

2 atoms of Hydrogen = 2(1.007) = 2.014 g
1 atom of Oxygen = 1(15.999) = 15.999 g

Total mass of H₂O = 18.013 g

%H = 2.014/18.013 = 11.2%
%O = 15.999/18.013 = 88.8%

Multiple Choice

Exercise 1: Given a 2.532 g sample of water. How many grams of the sample is hydrogen?

• 22.61 g

• 0.2836 g

• 2.248 g

• 2.851 g

Multiple Choice

Exercise 1: Given a 2.532 g sample of water. How many grams of the sample is Oxygen?

• 22.61 g

• 0.2836 g

• 2.248 g

• 2.851 g

Multiple Choice

Example 2: Pitchblende is the most important compound of uranium. Mass analysis of an 84.2 g sample shows that it contains 71.4 g of uranium, with oxygen being the only other element. How many grams of uranium are in 102 kg of pitchblende?

• 12.8 g

• 84.8 g

• 86.5 g

• 120 g

​Example 2: H₂O to H₂O₂

n H₂O the ratio of H: O atoms is 2:1
In H₂O₂ the ratio of H:O atoms is 2:2 or 1:1

small whole numbers

Multiple Choice

What law is observed or demonstrated in the following?

A sample of potassium chloride from Chili contains the same percent by mass of potassium as one from Poland

• Law of Conservation of Mass

• Law of Definite Proportions

• Law of Multiple Proportions

Multiple Choice

What law is observed or demonstrated in the following?

A flashbulb on the street corner of London, England contains magnesium and oxygen before use and magnesium oxide afterward, but its mass does not change.

• Law of Conservation of Mass

• Law of Definite Proportions

• Law of Multiple Proportions

Multiple Choice

What law is observed or demonstrated in the following?

Deep in the caves of Camuy in Puerto Rico contain large amounts of Arsenic. Upon observing the cave, his keen eye notices arsenic and oxygen from one compound that is 65.3 mass % arsenic and another that is 75.8 mass % arsenic.

• Law of Conservation of Mass

• Law of Definite Proportions

• Law of Multiple Proportions

Multiple Select

Which of the following are true according to Dalton's atomic theory?

• Atoms of one element cannot be changed into atoms of another element by chemical reactions.

• Atoms are created during chemical reactions.

• Compounds are formed when atoms of more than one element combine.

• All atoms of a given element are identical.

​Complete chart Protons, Neutron and Electrons

​Exercise #6

Chlorine has two naturally occurring isotopes
Cl-35: 34.969 amu, 75.77% abundance
Cl-37: 36.966 amu, 24.23% abundance

Calculate the average atomic mass.

Cl-35 34.969 (0.7577) = 26.50 (sig dig)
Cl-37 36.966 (0.2423) = 8.957
Atomic mass of Cl = 35.47 amu

Multiple Choice

Which model of the atom was proposed by Thomson around 1900, and what were its main features?

• Plum pudding model; positive sphere with embedded negative electrons

• Bohr model; electrons in fixed orbits

• Rutherford model; dense nucleus with electrons outside

• Quantum model; electrons in probability clouds

Multiple Choice

Which instrument is used to measure atomic and molecular weight with great accuracy?

• Mass spectrometer

• Electron microscope

• X-ray diffractometer

• Thermometer

Open Ended

Describe the experiment conducted by Rutherford that led to the discovery of the nucleus.

Open Ended

Explain the difference between atomic number and mass number, and describe how each is represented in the symbol of an element.

Multiple Choice

What observation from Rutherford's gold foil experiment contradicted Thomson's model of the atom?

• Some alpha particles were deflected at large angles

• All alpha particles passed straight through the foil

• Alpha particles were absorbed by the gold foil

• Electrons were found in the nucleus

Multiple Choice

Which of the following statements about isotopes is correct?

• Isotopes have the same number of protons but different numbers of neutrons.

• Isotopes have different numbers of protons and neutrons.

• Isotopes have the same number of neutrons but different numbers of protons.

• Isotopes have different numbers of electrons only.

Multiple Select

Which of the following statements about subatomic particles are correct?

• Protons and neutrons have nearly the same mass

• Electrons have a significant mass compared to protons

• Protons and neutrons are found in the nucleus

• Electrons are positively charged

Open Ended

How does the arrangement of elements in the periodic table differ from the way isotopes are written, and where are the atomic number and atomic weight shown in a periodic table box?

Open Ended

Explain why atomic mass units (amu) are used instead of grams to express the mass of atoms.

Multiple Select

Which of the following are true about the periodic table?

• Rows are called periods.

• Columns are called groups.

• Elements in the same group have similar chemical properties.

• Rows are called groups.

Multiple Choice

Which of the following statements is NOT part of Dalton's Atomic Theory?

• Atoms of one element can be changed into atoms of another element by chemical reactions.

• Each element is composed of extremely small particles called atoms.

• All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other elements.

• Compounds are formed when atoms of more than one element combine.

Open Ended

Summarize one key idea you learned today about Dalton's Atomic Theory and how it changed our understanding of matter.