2. Atoms & Elements

Atomic Mass

Atomic Mass: Introduction

Atomic Mass Example 3

What is Atomic Mass? | Don't Memorise

Measuring Atomic Mass | Atoms and Molecules | Don't Memorise

Silver has an atomic mass of 107.868 amu. The Ag-109 isotope (108.905 amu) is 48.16%. What is the amu of the other isotope?

Naturally occurring iodine has an atomic mass of 126.9045 amu.
A 12.3849 g sample of iodine is accidentally contaminated with
an additional 1.00070 g of 129I, a synthetic radioisotope of iodine
used in the treatment of certain diseases of the thyroid gland.
The mass of 129I is 128.9050 amu. Find the apparent “atomic
mass” of the contaminated iodine.

(a) The unified atomic mass unit (u) is used to represent the extremely small mass of atoms. How many grams are equivalent to 1 u?

Silver is composed of two naturally occurring isotopes: Ag-107
(51.839%) and Ag-109. The ratio of the masses of the two isotopes
is 1.0187. What is the mass of Ag-107?

Only three isotopes of magnesium exist on earth. 24Mg is the most common form at 78.70% natural abundance with a mass of 23.98504 amu, 25Mg has a 10.13% natural abundance, while 26Mg has a natural abundance of 11.17% and a mass of 25.98259 amu. What is the mass of the 25Mg isotope?

An element has four naturally occurring isotopes with the
masses and natural abundances given here. Find the atomic
mass of the element and identify it.
Isotope Mass (amu) Abundance (%)
1 135.90714 0.19
2 137.90599 0.25
3 139.90543 88.43
4 141.90924 11.13

The following diagram is a representation of 20 atoms of
a fictitious element, which we will call nevadium (Nv).
The red spheres are 293Nv, and the blue spheres are 295Nv.
(a) Assuming that this sample is a statistically representative
sample of the element, calculate the percent abundance
of each element. 
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/db4af71268dc84d9-1660559302386.jpg" alt="" />

(a) What isotope is used as the standard in establishing the
atomic mass scale?

A sample of naturally occurring silicon consists of 28^Si (27.9769), 29^Si (28.9765), and 30^Si (29.9738). If the atomic weight of silicon is 28.0855 and the natural abundance of 29^Si is 4.68%, what are the natural abundances of 28^Si and 30^Si?

Atomic Mass Example 1

On the Periodic Table, the atomic mass is represented by the number with decimal places.&nbsp;

Magnesium has three naturally occurring isotopes: 24^Mg (23.985) with 78.99% abundance, 25^Mg (24.986) with 10.00% abundance, and a third with 11.01% abundance. Look up the atomic weight of magnesium, and then calculate the mass of the third isotope.

Bromine has two naturally occurring isotopes, bromine-79
1atomic mass = 78.9183 u; abundance = 50.69%2 a n d
bromine-81 1atomic mass = 80.9163 u; abundance =
49.31%2. Calculate the atomic weight of bromine.

Relative Atomic Mass | Properties of Matter | Chemistry | FuseSchool

The following diagram is a representation of 20 atoms of 
a fictitious element, which we will call nevadium (Nv). 
The red spheres are 293Nv, and the blue spheres are 295Nv. 
(b) If the mass of 293Nv is 293.15 u and 
that of 295Nv is 295.15 u, what is the atomic weight of Nv? 
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/5466212bf9296b4d-1664218224498.jpg" alt="" />

Which of the following choices has the greatest atomic mass?

Periodic Table Trends

Iron has three major isotopes: 54Fe (atomic mass =
53.9396 u; abundance 5.85%), 56Fe (atomic mass =
55.9349 u; abundance 91.75%), and 57Fe (atomic
mass = 56.9354 u; abundance 2.12 %). Calculate the atomic
weight (average atomic mass) of iron.

The nucleus of 6Li is a powerful absorber of neutrons. It
exists in the naturally occurring metal to the extent of
7.5%. In the era of nuclear deterrence, large quantities
of lithium were processed to remove 6Li for use in hydrogen
bomb production. The lithium metal remaining after
removal of 6Li was sold on the market. (b) The atomic
masses of 6Li and 7Li are 6.015122 and 7.016004 u, respectively.
A sample of lithium depleted in the lighter isotope
was found on analysis to contain 1.442% 6Li. What is the
average atomic weight of this sample of the metal?

Naturally occurring chlorine is composed of two isotopes:
75.76% Cl-35 (mass 34.9688 amu) and 24.24% Cl-37 (mass
36.9659 amu). Naturally occurring oxygen is composed of three
isotopes: 99.757% O-16 (mass 15.9949 amu), 0.038% O-17
(mass 16.9991 amu), and 0.205% O-18 (mass 17.9991 amu). The
compound dichlorine monoxide is composed of two chlorine
atoms and one oxygen atom bonded together to form the Cl2O
molecule. How many Cl2O molecules of different masses naturally
exist? Give the masses of the three most abundant Cl2O
molecules.

Prior to 1961, the atomic mass unit (amu) was defined as 1/16 the mass of the atomic weight of oxygen; that is, the atomic weight of oxygen was defined as exactly 16. What was the mass of a 12C atom prior to 1961 if the atomic weight of oxygen on today’s scale is 15.9994?

Silicon has three naturally occurring isotopes (Si-28, Si-29, and
Si-30). The mass and natural abundance of Si-28 are 27.9769
amu and 92.2%, respectively. The mass and natural abundance
of Si-29 are 28.9765 amu and 4.67%, respectively. Find the mass
and natural abundance of Si-30.

Isotopes, Percent Abundance, Atomic Mass | How to Pass Chemistry

Atomic Mass Example 2

Bromine has two naturally occurring isotopes (Br-79 and Br-81)
and has an atomic mass of 79.904 amu. The mass of Br-81 is
80.9163 amu, and its natural abundance is 49.31%. Calculate
the mass and natural abundance of Br-79.

Copper metal has two naturally occurring isotopes: copper-63 (69.15%; isotopic mass = 62.93) and copper-65 (30.85%; isotopic mass 64.93). Calculate the atomic weight of copper, and check your answer in the periodic table.

Copper (Cu) consists of two naturally occurring isotopes with
masses of 62.9296 and 64.9278 u. (a) How many protons and
neutrons are in the nucleus of each isotope? Write the complete
atomic symbol for each, showing the atomic number and
mass number. (b) The average atomic mass of Cu is 63.55 u.
Calculate the abundance of each isotope.

Germanium has five naturally occurring isotopes: 70^Ge, 20.5%, 69.924; 72^Ge, 27.4%, 71.922; 73^Ge, 7.8%, 72.923; 74^Ge, 36.5%, 73.921; and 76^Ge, 7.8%, 75.921. What is the atomic weight of germanium?

Lithium has only two naturally occurring isotopes. The mass
of lithium-6 is 6.01512 amu and the mass of lithium-7
is 7.01601 amu. Calculate the relative abundances of the two
isotopes.

Naturally occurring silver consists of two isotopes: 107^Ag (51.84%) with an isotopic mass of 106.9051 and 109^Ag (48.16%) with an isotopic mass of 108.9048. What is the atomic weight of silver? Check your answer in a periodic table.

The element chromium (Cr) consists of four naturally occurring 
isotopes with atomic masses 49.9460, 51.9405, 52.9407, 
and 53.9389 u. The relative abundances of these four isotopes 
are 4.3, 83.8, 9.5, and 2.4%, respectively. From these 
data, calculate the atomic weight of chromium.

What is the difference between an element’s atomic number and its atomic weight?

There are two different isotopes of bromine atoms. Under
normal conditions, elemental bromine consists of Br2 molecules,
and the mass of a Br2 molecule is the sum of the masses
of the two atoms in the molecule. The mass spectrum of Br2
consists of three peaks:
Mass (u) Relative Size
157.836 0.2569
159.834 0.4999
161.832 0.2431
(b) What is the mass of each isotope?

Boron has only two naturally occurring isotopes. The mass of
boron-10 is 10.01294 amu and the mass of boron-11 is 11.00931
amu. Calculate the relative abundances of the two isotopes.

Atomic Number, Atomic Mass, and Mass Number!

An element has two naturally occurring isotopes. Isotope 1 has
a mass of 120.9038 amu and a relative abundance of 57.4%, and
isotope 2 has a mass of 122.9042 amu. Find the atomic mass of
this element and identify it.

Isotopes and Atomic Mass

What is the atomic weight of an element that consists of two naturally occurring isotopes? The first isotope has a mass of 84.911 and an abundance of 72.17% and the second isotope has a mass of 86.909 and an abundance of 27.83%. (LO 2.15)
(a) 85.47 
(b) 86.35 
(c) 85.91 
(d) 85.17

(b) Why is the atomic weight of carbon reported as 12.011 in the table
of elements and the periodic table in the front inside cover of
this text?

The unified atomic mass unit (u) 1/12 the mass of a neutral atom of:
(a) 1^H
(b) 12^C 
(c) 14^C
(d) 16^O

Iodine has a lower atomic mass than tellurium (126.90 for iodine, 127.60 for tellurium) even though it has a higher atomic number (53 for iodine, 52 for tellurium). Explain.

Naturally occurring boron consists of two isotopes: 10^B (19.9%) with an isotopic mass of 10.0129 and 11^B (80.1%) with an isotopic mass of 11.009 31. What is the atomic weight of boron? Check your answer by looking at a periodic table.

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1. Intro to General Chemistry

3. Chemical Reactions

4. BONUS: Lab Techniques and Procedures

5. BONUS: Mathematical Operations and Functions

6. Chemical Quantities & Aqueous Reactions

7. Gases

8. Thermochemistry

9. Quantum Mechanics

10. Periodic Properties of the Elements

11. Bonding & Molecular Structure

12. Molecular Shapes & Valence Bond Theory

13. Liquids, Solids & Intermolecular Forces

14. Solutions

15. Chemical Kinetics

16. Chemical Equilibrium

17. Acid and Base Equilibrium

18. Aqueous Equilibrium

19. Chemical Thermodynamics

20. Electrochemistry

21. Nuclear Chemistry

22. Organic Chemistry

23. Chemistry of the Nonmetals

24. Transition Metals and Coordination Compounds

[BOOK CHEM] Clutch Version

Millikan Oil Drop Experiment

The Oil Drop Experiment helped with determining the fundamental charge of the electron.&nbsp;

Ions

Ions represent elements that possess either a positive charge or a negative charge.&nbsp;

Periodic Table: Charges

Elements lose or gain electrons to have the ideal number of outer shell electrons like the noble gases.&nbsp;

Law of Definite Proportions

"Different samples of a pure chemical compound always contain the same proportions of elements by mass."

Periodic Table: Classifications

The Periodic Table contains 3 Major Classifications when describing its elements

Isotopes

Isotopes are atoms of an element that have the same atomic number, but different mass number.&nbsp;

The Atom

The atom represents the basic functional unit in chemistry

Mole Concept

The Mole Concept involves the interconversions between different unit amounts of a substance.

Periodic Table: Representative Elements & Transition Metals

The Groups of the Periodic Table can be broken down into the Representative Elements and Transition Metals

Atomic Theory

John Dalton, one of the "Fathers of Chemistry"is credited with modernizing the Atomic Theory.

Subatomic Particles

The atom is composed of 3 subatomic particles:neutrons, protons, and electrons.

Periodic Table: Elemental Forms

The elements of the Periodic Table exist in different elemental forms in the natural world

Periodic Table: Phases

Under standard conditions of temperature and pressure, the elements can exist as solids, liquids or gases

The atomic mass of an element includes the masses of all 3 subatomic particles of neutrons, protons and electrons.&nbsp;

Periodic Table: Group Names

The Periodic Table can be further classified into Periods and Groups.&nbsp;

Law of Conservation of Mass

"In a chemical reaction, no matter is created or destroyed, but instead changes form."

Calculating Molar Mass

Molar Mass is a physical property that represents the mass of a substance divided by the amount of that substance.

Rutherford Gold Foil Experiment

The Gold Foil Experiment helped with the discovery of the positively charged nucleus.

Law of Multiple Proportions

“When 2 elements (A &amp; B) form different compounds, the mass of Element B that combine with 1 g of A are a ratio of whole numbers."

Periodic Table: Element Symbols

The Element Symbols of the Periodic Table represent the abbreviated form of an element