Comprehensive Study Guide: Atomic Structure, Isotope Notation, and the Periodic Table of the Elements

Fundamental Vocabulary and Subatomic Particles

• Subatomic Particle Characteristics and Spatial Distribution:

  • Proton: A positively charged subatomic particle ($+1$ relative charge) situated inside the dense central nucleus of an atom. Protons have a relative mass of approximately $1\,\text{amu}$ and constitute most of the atom's mass alongside neutrons. The number of protons defines the atomic number ($Z$) and dictates the elemental identity of the atom; two atoms of the same element always contain the exact same number of protons.
  • Neutron: An electrically neutral subatomic particle ($0$ net charge) located within the nucleus. Neutrons possess a relative mass approximately equal to that of a proton ($\approx 1\,\text{amu}$). Together with protons, neutrons account for virtually all of an atom's physical mass.
  • Electron: A negatively charged subatomic particle ($-1$ relative charge) located outside the nucleus in regions called electron shells, energy levels, or the electron cloud. Electrons possess negligible mass compared to nucleons (protons and neutrons) and contribute minimally to the total mass of the atom.
  • Nucleus: The dense, positively charged core at the center of the atom. The nucleus contains only protons and neutrons, packing nearly all of the atom's mass into an extremely compact volume.
  • Valence Electrons: The electrons occupying the outermost energy level (valence shell) of an atom. Valence electrons are the primary subatomic particles that participate in chemical bonding, reactivity, and compound formation.
  • Core Electrons: The inner electrons situated between the nucleus and the valence shell that do not directly participate in chemical bonding.

• Atomic Forces and Stability:

  • Electrostatic Attraction: The primary attractive force holding an atom together is the electromagnetic force between opposite electrical charges. The positively charged protons within the nucleus exert an electrostatic pull on the negatively charged electrons residing in the surrounding electron cloud.
  • Subatomic Interactions: Positively charged protons experience electrostatic repulsion from other protons, requiring the strong nuclear force mediated by neutrons to maintain nuclear stability, whereas gravitational forces between subatomic particles (such as electrons and neutrons) are negligibly weak.

Atomic Structure and Historical Models

• Evolution of Atomic Models:

  • Dalton's Solid Sphere Model: Conceptualized the atom as an indivisible, uniform solid sphere with no internal subatomic components.
  • J.J. Thomson's Plum Pudding Model: The first historical atomic model to identify and incorporate subatomic particles by demonstrating that atoms contain tiny, negatively charged particles designated as electrons, distributed within a sea of positive charge.
  • Rutherford's Nuclear Model: Introduced following the gold foil experiment, demonstrating that an atom is mostly empty space with a dense, positively charged nucleus at its center containing the mass.
  • Bohr Model: Depicts the atom with a central nucleus consisting of protons and neutrons, encircled by electrons traveling in concentric, circular orbits situated at fixed distances and energy levels.
  • Electron Cloud Model (Modern Quantum Mechanical Model): Proposes that electrons do not travel in rigid, fixed circular paths; rather, they exist within regions of probability designated as electron clouds, orbitals, shells, or quantized energy levels surrounding the nucleus.

• Electron Shell Capacities and Filling Rules (Bohr System):

  • Energy Level Filling Sequence: Electrons systematically occupy the innermost energy levels (closest to the nucleus) first before populating outer energy levels.
  • First Energy Level Maximum Capacity: The innermost energy level ($n = 1$) can hold a maximum of $2$ electrons.
  • Classroom Bohr Shell Progression: The sequential capacity pattern of electrons that can be held across consecutive energy levels follows the configuration: $2, 8, 18, 8$.

Atomic Number, Mass Number, and Isotope Calculations

• Mathematical Relationships in Atomic Structure:

  • Atomic Number ($Z$): Equivalent to the number of protons in an atom. In an electrically neutral atom, the atomic number also equals the number of electrons:     $\text{Atomic Number} = \text{Number of Protons}$
  • Mass Number ($A$): The total integer sum of protons and neutrons located in the nucleus:     $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$
  • Neutron Number Calculation: The quantity of neutrons within an atom is calculated by subtracting the atomic number from the mass number:     $\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}$

• Worked Examples for Particle Counting:

  • Example 1 (Finding Mass Number): An atom containing $11$ protons and $12$ neutrons has a mass number equal to:     $\text{Mass Number} = 11 + 12 = 23$
  • Example 2 (Finding Neutrons from Mass and Atomic Number): An atom with atomic number $11$ and mass number $23$ contains:     $\text{Number of Neutrons} = 23 - 11 = 12$
  • Example 3 (Isotopic Particle Counting for Iron): For the isotope $^{56}_{26}\text{Fe}$, where the atomic number is $26$ and the mass number is $56$:     $\text{Number of Neutrons} = 56 - 26 = 30$

• Isotopes and Chemical Notation:

  • Definition of Isotopes: Isotopes are atoms of the identical chemical element that possess the exact same number of protons (same atomic number) but distinct numbers of neutrons, resulting in different mass numbers.
  • Determination of Isotopes: Isotopes are identified by measuring or comparing their mass numbers or neutron counts while verifying that their proton count remains identical. For example, carbon exists as carbon-$12$ ($6$ protons and $6$ neutrons) and carbon-$14$ ($6$ protons and $8$ neutrons); chlorine naturally exists as chlorine-$35$ and chlorine-$37$.
  • Hyphen Notation: The element name or symbol followed directly by a hyphen and the mass number ($A$):     $\text{Element Name}-\text{Mass Number}$
  • Examples: Potassium-$40$, Chlorine-$35$, Carbon-$12$.
  • Nuclear Notation (Isotope Symbol): Written using the element symbol accompanied by the mass number ($A$) as a leading superscript and the atomic number ($Z$) as a leading subscript:     $^{A}_{Z}\text{X}$
  • For an isotope with mass number $35$ and $17$ protons: Hyphen notation is Chlorine-$35$; nuclear notation is $^{35}_{17}\text{Cl}$.
  • For Potassium-$40$ ($19$ protons, mass number $40$): Nuclear notation is $^{40}_{19}\text{K}$.
  • For Iron-$56$ ($26$ protons, mass number $56$): Nuclear notation is $^{56}_{26}\text{Fe}$.

• Average Atomic Mass:

  • Nature of Tabulated Atomic Masses: The atomic mass displayed on the periodic table is not an integer because it represents a weighted average of the masses of all naturally occurring stable and long-lived isotopes of that element, factored by their natural relative abundances.
  • Case Study (Chlorine): Chlorine has an average atomic mass of approximately $35.45\,\text{amu}$. This decimal value does not mean any individual chlorine atom weighs $35.45\,\text{amu}$; rather, it reflects a naturally occurring isotopic mixture primarily composed of chlorine-$35$ ($\approx 75.77\%$ abundance) and chlorine-$37$ ($\approx 24.23\%$ abundance).

The Periodic Table of the Elements: Organization, Trends, and Anatomy

• Organizational Framework:

  • Atomic Number Progression: The periodic table organizes all chemical elements in ascending order of atomic number ($Z$), beginning with Hydrogen ($Z = 1$) and continuing sequentially through Oganesson ($Z = 118$).
  • Periodic Law: When arranged by atomic number, elements display a periodic recurrence of similar physical and chemical properties.
  • Groups (Families): The vertical columns of the table. Elements within the same group possess the identical number of valence electrons in their outermost shell, which causes them to exhibit similar chemical reactivities and bonding behaviors.
  • Periods: The horizontal rows of the table. The period number corresponds to the highest occupied principal energy level (electron shell) of the elements in that row.

• Anatomy of a Standard Periodic Table Tile:

  • Atomic Number: Positioned at the top center of each cell; indicates the total proton count.
  • Element Symbol: Displayed as a large one- or two-letter abbreviation in the center (e.g., $\text{H}$, $\text{He}$, $\text{Li}$, $\text{Be}$).
  • Element Name: Printed directly below the elemental symbol (e.g., Hydrogen, Helium, Lithium, Beryllium).
  • Average Atomic Mass: Tabulated at the bottom of the tile as a decimal value representing the abundance-weighted isotopic mass (or bracketed integer for unstable, synthetic radioisotopes).

• Positional Classifications and Structural Blocks:

  • Hydrogen ($\text{H}$, $Z = 1$, Average Atomic Mass $1.01\,\text{amu}$): Classified chemically as a nonmetal, yet situated in Period 1, Group 1 on the far left side of the table above alkali metals. This placement constitutes a structural exception based on its single valence electron ($1s^1$ configuration).
  • Metals, Nonmetals, and Metalloids:
  • Metals predominate on the left and center regions of the periodic table.
  • Nonmetals reside predominantly on the upper right side of the periodic table (with the sole exception of Hydrogen on the upper left).
  • Metalloids form a diagonal boundary separating metals from nonmetals.
  • Inner Transition Metals (Lanthanides and Actinides):
  • Lanthanide Series: Positioned in an auxiliary row detached below the main body, extending from Cerium ($\text{Ce}$, $Z = 58$, $140.12\,\text{amu}$) through Lutetium ($\text{Lu}$, $Z = 71$, $174.97\,\text{amu}$), following Lanthanum ($\text{La}$, $Z = 57$, $138.91\,\text{amu}$).
  • Actinide Series: Situated directly below the lanthanides, extending from Thorium ($\text{Th}$, $Z = 90$, $232.04\,\text{amu}$) through Lawrencium ($\text{Lr}$, $Z = 103$, $[262]\,\text{amu}$), following Actinium ($\text{Ac}$, $Z = 89$, $[227]\,\text{amu}$).

• Complete Elemental Inventory from Reference Periodic Table:

  • Period 1:
  • Group 1: Hydrogen ($\text{H}$, $Z = 1$, mass $1.01$\text{ amu})
  • Group 18: Helium ($\text{He}$, $Z = 2$, mass $4.00$\text{ amu})
  • Period 2:
  • Group 1: Lithium ($\text{Li}$, $Z = 3$, mass $6.94$\text{ amu})
  • Group 2: Beryllium ($\text{Be}$, $Z = 4$, mass $9.01$\text{ amu})
  • Group 13: Boron ($\text{B}$, $Z = 5$, mass $10.81$\text{ amu})
  • Group 14: Carbon ($\text{C}$, $Z = 6$, mass $12.01$\text{ amu})
  • Group 15: Nitrogen ($\text{N}$, $Z = 7$, mass $14.01$\text{ amu})
  • Group 16: Oxygen ($\text{O}$, $Z = 8$, mass $16.00$\text{ amu})
  • Group 17: Fluorine ($\text{F}$, $Z = 9$, mass $19.00$\text{ amu})
  • Group 18: Neon ($\text{Ne}$, $Z = 10$, mass $20.18$\text{ amu})
  • Period 3:
  • Group 1: Sodium ($\text{Na}$, $Z = 11$, mass $22.99$\text{ amu})
  • Group 2: Magnesium ($\text{Mg}$, $Z = 12$, mass $24.31$\text{ amu})
  • Group 13: Aluminum ($\text{Al}$, $Z = 13$, mass $26.98$\text{ amu})
  • Group 14: Silicon ($\text{Si}$, $Z = 14$, mass $28.09$\text{ amu})
  • Group 15: Phosphorus ($\text{P}$, $Z = 15$, mass $30.97$\text{ amu})
  • Group 16: Sulfur ($\text{S}$, $Z = 16$, mass $32.07$\text{ amu})
  • Group 17: Chlorine ($\text{Cl}$, $Z = 17$, mass $35.45$\text{ amu})
  • Group 18: Argon ($\text{Ar}$, $Z = 18$, mass $39.95$\text{ amu})
  • Period 4:
  • Group 1: Potassium ($\text{K}$, $Z = 19$, mass $39.10$\text{ amu})
  • Group 2: Calcium ($\text{Ca}$, $Z = 20$, mass $40.08$\text{ amu})
  • Group 3: Scandium ($\text{Sc}$, $Z = 21$, mass $44.96$\text{ amu})
  • Group 4: Titanium ($\text{Ti}$, $Z = 22$, mass $47.87$\text{ amu})
  • Group 5: Vanadium ($\text{V}$, $Z = 23$, mass $50.94$\text{ amu})
  • Group 6: Chromium ($\text{Cr}$, $Z = 24$, mass $52.00$\text{ amu})
  • Group 7: Manganese ($\text{Mn}$, $Z = 25$, mass $54.94$\text{ amu})
  • Group 8: Iron ($\text{Fe}$, $Z = 26$, mass $55.85$\text{ amu})
  • Group 9: Cobalt ($\text{Co}$, $Z = 27$, mass $58.93$\text{ amu})
  • Group 10: Nickel ($\text{Ni}$, $Z = 28$, mass $58.69$\text{ amu})
  • Group 11: Copper ($\text{Cu}$, $Z = 29$, mass $63.55$\text{ amu})
  • Group 12: Zinc ($\text{Zn}$, $Z = 30$, mass $65.41$\text{ amu})
  • Group 13: Gallium ($\text{Ga}$, $Z = 31$, mass $69.72$\text{ amu})
  • Group 14: Germanium ($\text{Ge}$, $Z = 32$, mass $72.64$\text{ amu})
  • Group 15: Arsenic ($\text{As}$, $Z = 33$, mass $74.92$\text{ amu})
  • Group 16: Selenium ($\text{Se}$, $Z = 34$, mass $78.96$\text{ amu})
  • Group 17: Bromine ($\text{Br}$, $Z = 35$, mass $79.90$\text{ amu})
  • Group 18: Krypton ($\text{Kr}$, $Z = 36$, mass $83.80$\text{ amu})
  • Period 5:
  • Group 1: Rubidium ($\text{Rb}$, $Z = 37$, mass $85.47$\text{ amu})
  • Group 2: Strontium ($\text{Sr}$, $Z = 38$, mass $87.62$\text{ amu})
  • Group 3: Yttrium ($\text{Y}$, $Z = 39$, mass $88.91$\text{ amu})
  • Group 4: Zirconium ($\text{Zr}$, $Z = 40$, mass $91.22$\text{ amu})
  • Group 5: Niobium ($\text{Nb}$, $Z = 41$, mass $92.91$\text{ amu})
  • Group 6: Molybdenum ($\text{Mo}$, $Z = 42$, mass $95.94$\text{ amu})
  • Group 7: Technetium ($\text{Tc}$, $Z = 43$, mass $[98]$\text{ amu})
  • Group 8: Ruthenium ($\text{Ru}$, $Z = 44$, mass $101.07$\text{ amu})
  • Group 9: Rhodium ($\text{Rh}$, $Z = 45$, mass $102.91$\text{ amu})
  • Group 10: Palladium ($\text{Pd}$, $Z = 46$, mass $106.42$\text{ amu})
  • Group 11: Silver ($\text{Ag}$, $Z = 47$, mass $107.87$\text{ amu})
  • Group 12: Cadmium ($\text{Cd}$, $Z = 48$, mass $112.41$\text{ amu})
  • Group 13: Indium ($\text{In}$, $Z = 49$, mass $114.82$\text{ amu})
  • Group 14: Tin ($\text{Sn}$, $Z = 50$, mass $118.71$\text{ amu})
  • Group 15: Antimony ($\text{Sb}$, $Z = 51$, mass $121.76$\text{ amu})
  • Group 16: Tellurium ($\text{Te}$, $Z = 52$, mass $127.60$\text{ amu})
  • Group 17: Iodine ($\text{I}$, $Z = 53$, mass $126.90$\text{ amu})
  • Group 18: Xenon ($\text{Xe}$, $Z = 54$, mass $131.29$\text{ amu})
  • Period 6:
  • Group 1: Cesium ($\text{Cs}$, $Z = 55$, mass $132.91$\text{ amu})
  • Group 2: Barium ($\text{Ba}$, $Z = 56$, mass $137.33$\text{ amu})
  • Group 3: Lanthanum ($\text{La}$, $Z = 57$, mass $138.91$\text{ amu})
  • Group 4: Hafnium ($\text{Hf}$, $Z = 72$, mass $178.49$\text{ amu})
  • Group 5: Tantalum ($\text{Ta}$, $Z = 73$, mass $180.95$\text{ amu})
  • Group 6: Tungsten ($\text{W}$, $Z = 74$, mass $183.84$\text{ amu})
  • Group 7: Rhenium ($\text{Re}$, $Z = 75$, mass $186.21$\text{ amu})
  • Group 8: Osmium ($\text{Os}$, $Z = 76$, mass $190.23$\text{ amu})
  • Group 9: Iridium ($\text{Ir}$, $Z = 77$, mass $192.22$\text{ amu})
  • Group 10: Platinum ($\text{Pt}$, $Z = 78$, mass $195.08$\text{ amu})
  • Group 11: Gold ($\text{Au}$, $Z = 79$, mass $196.97$\text{ amu})
  • Group 12: Mercury ($\text{Hg}$, $Z = 80$, mass $200.59$\text{ amu})
  • Group 13: Thallium ($\text{Tl}$, $Z = 81$, mass $204.38$\text{ amu})
  • Group 14: Lead ($\text{Pb}$, $Z = 82$, mass $207.2$\text{ amu})
  • Group 15: Bismuth ($\text{Bi}$, $Z = 83$, mass $208.98$\text{ amu})
  • Group 16: Polonium ($\text{Po}$, $Z = 84$, mass $[209]$\text{ amu})
  • Group 17: Astatine ($\text{At}$, $Z = 85$, mass $[210]$\text{ amu})
  • Group 18: Radon ($\text{Rn}$, $Z = 86$, mass $[222]$\text{ amu})
  • Period 7:
  • Group 1: Francium ($\text{Fr}$, $Z = 87$, mass $[223]$\text{ amu})
  • Group 2: Radium ($\text{Ra}$, $Z = 88$, mass $[226]$\text{ amu})
  • Group 3: Actinium ($\text{Ac}$, $Z = 89$, mass $[227]$\text{ amu})
  • Group 4: Rutherfordium ($\text{Rf}$, $Z = 104$, mass $[267]$\text{ amu})
  • Group 5: Dubnium ($\text{Db}$, $Z = 105$, mass $[268]$\text{ amu})
  • Group 6: Seaborgium ($\text{Sg}$, $Z = 106$, mass $[269]$\text{ amu})
  • Group 7: Bohrium ($\text{Bh}$, $Z = 107$, mass $[270]$\text{ amu})
  • Group 8: Hassium ($\text{Hs}$, $Z = 108$, mass $[270]$\text{ amu})
  • Group 9: Meitnerium ($\text{Mt}$, $Z = 109$, mass $[278]$\text{ amu})
  • Group 10: Darmstadtium ($\text{Ds}$, $Z = 110$, mass $[281]$\text{ amu})
  • Group 11: Roentgenium ($\text{Rg}$, $Z = 111$, mass $[282]$\text{ amu})
  • Group 12: Copernicium ($\text{Cn}$, $Z = 112$, mass $[285]$\text{ amu})
  • Group 13: Nihonium ($\text{Nh}$, $Z = 113$, mass $[286]$\text{ amu})
  • Group 14: Flerovium ($\text{Fl}$, $Z = 114$, mass $[289]$\text{ amu})
  • Group 15: Moscovium ($\text{Mc}$, $Z = 115$, mass $[290]$\text{ amu})
  • Group 16: Livermorium ($\text{Lv}$, $Z = 116$, mass $[293]$\text{ amu})
  • Group 17: Tennessine ($\text{Ts}$, $Z = 117$, mass $[294]$\text{ amu})
  • Group 18: Oganesson ($\text{Og}$, $Z = 118$, mass $[294]$\text{ amu})
  • Lanthanide Series ($Z = 58$ to $71$):
  • Cerium ($\text{Ce}$, $Z = 58$, mass $140.12$\text{ amu})
  • Praseodymium ($\text{Pr}$, $Z = 59$, mass $140.91$\text{ amu})
  • Neodymium ($\text{Nd}$, $Z = 60$, mass $144.24$\text{ amu})
  • Promethium ($\text{Pm}$, $Z = 61$, mass $[145]$\text{ amu})
  • Samarium ($\text{Sm}$, $Z = 62$, mass $150.36$\text{ amu})
  • Europium ($\text{Eu}$, $Z = 63$, mass $151.96$\text{ amu})
  • Gadolinium ($\text{Gd}$, $Z = 64$, mass $157.25$\text{ amu})
  • Terbium ($\text{Tb}$, $Z = 65$, mass $158.93$\text{ amu})
  • Dysprosium ($\text{Dy}$, $Z = 66$, mass $162.50$\text{ amu})
  • Holmium ($\text{Ho}$, $Z = 67$, mass $164.93$\text{ amu})
  • Erbium ($\text{Er}$, $Z = 68$, mass $167.26$\text{ amu})
  • Thulium ($\text{Tm}$, $Z = 69$, mass $168.93$\text{ amu})
  • Ytterbium ($\text{Yb}$, $Z = 70$, mass $173.04$\text{ amu})
  • Lutetium ($\text{Lu}$, $Z = 71$, mass $174.97$\text{ amu})
  • Actinide Series ($Z = 90$ to $103$):
  • Thorium ($\text{Th}$, $Z = 90$, mass $232.04$\text{ amu})
  • Protactinium ($\text{Pa}$, $Z = 91$, mass $231.04$\text{ amu})
  • Uranium ($\text{U}$, $Z = 92$, mass $238.03$\text{ amu})
  • Neptunium ($\text{Np}$, $Z = 93$, mass $[237]$\text{ amu})
  • Plutonium ($\text{Pu}$, $Z = 94$, mass $[244]$\text{ amu})
  • Americium ($\text{Am}$, $Z = 95$, mass $[243]$\text{ amu})
  • Curium ($\text{Cm}$, $Z = 96$, mass $[247]$\text{ amu})
  • Berkelium ($\text{Bk}$, $Z = 97$, mass $[247]$\text{ amu})
  • Californium ($\text{Cf}$, $Z = 98$, mass $[251]$\text{ amu})
  • Einsteinium ($\text{Es}$, $Z = 99$, mass $[252]$\text{ amu})
  • Fermium ($\text{Fm}$, $Z = 100$, mass $[257]$\text{ amu})
  • Mendelevium ($\text{Md}$, $Z = 101$, mass $[258]$\text{ amu})
  • Nobelium ($\text{No}$, $Z = 102$, mass $[259]$\text{ amu})
  • Lawrencium ($\text{Lr}$, $Z = 103$, mass $[262]$\text{ amu})
  • Publication Credit: Table formatted and produced by Serina Gay of Mrs. Gay's Classroom - Teachers Pay Teachers 2019.

Study Guide Practice Questions and Worked Solutions

• Subatomic Particle Distributions and Forces:

  • Question 1: Which statement correctly describes the location and charge of subatomic particles?
  • A. Protons are in the electron cloud and are negative.
  • B. Neutrons are in the nucleus and have no charge.
  • C. Electrons are in the nucleus and are positive.
  • D. Protons are outside the nucleus and are neutral.
  • Correct Answer: B. Neutrons are in the nucleus and have no charge. Protons ($+1$ charge) and neutrons ($0$ charge) reside strictly inside the nucleus, whereas electrons ($-1$ charge) occupy orbitals within the electron cloud outside the nucleus.
  • Question 2: The nucleus of an atom contains:
  • A. Only electrons.
  • B. Protons and neutrons.
  • C. Electrons and protons.
  • D. Only protons.
  • Correct Answer: B. Protons and neutrons. Together these nucleons provide nearly all the mass of the atom.
  • Question 3: Which subatomic particle determines the identity of the element?
  • A. Electron
  • B. Neutron
  • C. Proton
  • D. Valence electron
  • Correct Answer: C. Proton. The proton count is the atomic number ($Z$), which uniquely identifies every element.
  • Question 4: Electrons that participate in chemical bonding are called:
  • A. Core electrons
  • B. Valence electrons
  • C. Neutrons
  • D. Nuclear electrons
  • Correct Answer: B. Valence electrons. Located in the outermost energy level, valence electrons interact during chemical reactions to form chemical bonds.
  • Question 5: According to the electron cloud model, electrons:
  • A. Travel in fixed circular orbits only.
  • B. Are found in regions of probability called shells or energy levels.
  • C. Are stuck to the nucleus and cannot move.
  • D. Are larger than protons.
  • Correct Answer: B. Are found in regions of probability called shells or energy levels. Quantum mechanics treats electron locations as probability distributions rather than predetermined deterministic paths.
  • Question 6: Which force helps hold the atom together by attracting electrons to the nucleus?
  • A. Repulsive force between protons
  • B. Attractive force between opposite charges
  • C. Gravity between electrons and neutrons
  • D. Repulsion between neutrons
  • Correct Answer: B. Attractive force between opposite charges. The positive charge of nuclear protons attracts the negatively charged electrons.

• Atomic Identity, Mass, and Historical Models:

  • Question 7: Two atoms of the same element always have the same number of:
  • A. Neutrons
  • B. Electrons in the outer shell
  • C. Protons
  • D. Isotopes
  • Correct Answer: C. Protons. Changing the number of protons changes the identity of the element.
  • Question 8: Which historical model first proposed that atoms contain small, negatively charged particles (electrons)?
  • A. Dalton's solid sphere model
  • B. Bohr model
  • C. Rutherford's nuclear model
  • D. J.J. Thomson's model
  • Correct Answer: D. J.J. Thomson's model. Thomson discovered the electron using cathode ray tubes and integrated it into his plum pudding model.
  • Question 9: Which choice correctly pairs the subatomic particle with its approximate contribution to mass and charge?
  • A. Electron - most mass, neutral charge
  • B. Neutron - very little mass, negative charge
  • C. Proton - most mass, positive charge
  • D. Proton and neutron - most of the atom's mass; proton is positive, neutron is neutral
  • Correct Answer: D. Proton and neutron - most of the atom's mass; proton is positive, neutron is neutral. Electrons contribute negligible mass and have a negative charge.
  • Question 10: If an atom has $11$ protons and $12$ neutrons, its mass number is:
  • A. $11$
  • B. $12$
  • C. $23$
  • D. $1$
  • Correct Answer: C. 23. Evaluated as:       $\text{Mass Number} = 11 + 12 = 23$
  • Question 11 (Free Response): How do we determine an isotope? Give an example with an element.
  • Explanation: An isotope is determined by comparing atoms of the same element that have the same atomic number (number of protons) but different mass numbers due to possessing different numbers of neutrons. For example, carbon always has $6$ protons, but carbon-$12$ has $6$ neutrons ($\text{mass number} = 12$) while carbon-$14$ has $8$ neutrons ($\text{mass number} = 14$).
  • Question 12 (Free Response): Write the following isotope in nuclear and hyphen notation: Mass number $35$ and protons $17$.
  • Hyphen notation: Chlorine-$35$
  • Nuclear notation: $^{35}_{17}\text{Cl}$
  • Question 13: An atom has atomic number $11$ and mass number $23$. How many neutrons does it have?
  • A. $11$
  • B. $12$
  • C. $23$
  • D. $34$
  • Correct Answer: B. 12. Evaluated as:       $\text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 23 - 11 = 12$

• Isotope Notation, Periodic Table Trends, and Bohr Systems:

  • Question 14: Potassium-$40$ is written in hyphen form. Which nuclear notation shows the same isotope? (Potassium atomic number = $19$)
  • A. $^{19}_{40}\text{K}$
  • B. $^{40}_{19}\text{K}$
  • C. $^{59}_{19}\text{K}$
  • D. $^{21}_{19}\text{K}$
  • Correct Answer: B. $^{40}_{19}\text{K}$. Mass number ($40$) is placed as the superscript, and atomic number ($19$) as the subscript.
  • Question 15: An unknown isotope is written as $^{56}_{26}\text{Fe}$. Using the periodic table (Fe atomic number = $26$), how many neutrons are in this isotope?
  • A. $26$
  • B. $30$
  • C. $56$
  • D. $82$
  • Correct Answer: B. 30. Evaluated as:       $\text{Neutrons} = 56 - 26 = 30$
  • Question 16: The average atomic mass of chlorine on the periodic table is about $35.45$. Which idea best explains this value?
  • A. Chlorine atoms all have mass number $35.45$.
  • B. The periodic table value is the mass of the lightest chlorine isotope.
  • C. The average atomic mass is a weighted average of chlorine's natural isotopes.
  • D. Chlorine atoms have equal numbers of protons and neutrons.
  • Correct Answer: C. The average atomic mass is a weighted average of chlorine's natural isotopes. Naturally occurring chlorine consists of an isotopic mixture containing mostly chlorine-$35$ with a smaller percentage of chlorine-$37$.
  • Question 17: Which calculation correctly finds the number of neutrons in an atom?
  • A. $\text{Neutrons} = \text{mass number} + \text{atomic number}$
  • B. $\text{Neutrons} = \text{atomic number} - \text{mass number}$
  • C. $\text{Neutrons} = \text{mass number} - \text{atomic number}$
  • D. $\text{Neutrons} = \text{number of electrons} - \text{atomic number}$
  • Correct Answer: C. $\text{Neutrons} = \text{mass number} - \text{atomic number}$.
  • Question 18: What does the periodic table organize?
  • A. Elements by atomic number and chemical properties
  • B. Atoms by their size only
  • C. Compounds by their color
  • D. Rocks by where they are found
  • Correct Answer: A. Elements by atomic number and chemical properties.
  • Question 19: What are valence electrons?
  • A. Electrons inside the nucleus
  • B. Electrons in the outermost energy level
  • C. Protons in the atom
  • D. Neutrons in the atom
  • Correct Answer: B. Electrons in the outermost energy level.
  • Question 20: Why do elements in the same group often have similar chemical properties?
  • A. They have the same mass number.
  • B. They have the same number of valence electrons.
  • C. They have the same number of neutrons.
  • D. They are all metals.
  • Correct Answer: B. They have the same number of valence electrons. Chemical reactivity is determined by valence shell interactions.
  • Question 30: In a Bohr model, where are protons and neutrons located?
  • A. In the nucleus
  • B. In the outermost energy level
  • C. Outside the electron cloud
  • D. In the periodic table group
  • Correct Answer: A. In the nucleus.
  • Question 31: In the classroom Bohr model system, how many electrons can the first energy level hold?
  • A. $1$
  • B. $2$
  • C. $8$
  • D. $18$
  • Correct Answer: B. 2. The first shell ($n = 1$) saturates at two electrons.
  • Question 32: When drawing a Bohr model, electrons should fill which energy levels first?
  • A. The outermost levels
  • B. The innermost levels
  • C. Only the second level
  • D. The levels with the most space
  • Correct Answer: B. The innermost levels. Electrons fill energy levels in order of lowest to highest energy.
  • Question 33: Which statement correctly describes hydrogen's location among nonmetals?
  • A. Hydrogen is on the right side with most nonmetals.
  • B. Hydrogen is a nonmetal, but it is an exception because it is on the left side.
  • C. Hydrogen is a metalloid in group $17$.
  • D. Hydrogen is a noble gas in group $18$.
  • Correct Answer: B. Hydrogen is a nonmetal, but it is an exception because it is on the left side.
  • Question 34: Identify the pattern of electrons that can be held in each shell?
  • A. $2, 18, 8, 8$
  • B. $1, 2, 8, 8$
  • C. $2, 8, 18, 8$
  • D. $2, 8, 8, 18$
  • Correct Answer: C. $2, 8, 18, 8$.