Unit 1 Test Notes Flashcards
What is the smallest possible particle of an element?
An atom
Atoms are the fundamental building blocks of matter.
What is a stable octet?
A full shell of eight electrons in the outer energy level of an atom
How do metal atoms in Groups 1, 2, or 3 achieve a stable octet?
They lose electrons to form cations
How do non-metal atoms in Groups 15, 16, or 17 achieve a stable octet?
They gain electrons to form anions
What are cations?
Positively charged ions that have lost electrons
What are anions?
Negatively charged ions that have gained electrons
What is the atomic number (Z)?
The number of protons in one atom of a specific element
What is atomic mass?
The average mass of an element, expressed in atomic mass units (amu)
How is atomic mass calculated?
of protons + # of neutrons
What are the charges of protons, electrons, and neutrons?
- Proton: 1+
- Electron: 1-
- Neutron: 0
What does an isotope represent?
Atoms with the same number of protons but a different number of neutrons
What is isotopic abundance?
The percentage of a given isotope in a sample of an element
Fill in the blank: Atomic mass is a _______ average of all the isotopes of the element.
weighted
True or False: All isotopes of an element have the same atomic mass.
False
What is a mass spectrometer used for?
To determine the relative abundance of each isotope
What are the three types of particles emitted by radioisotopes?
- Alpha particles
- Beta particles
- Gamma rays
How do you calculate the atomic mass given isotopic abundance?
atomic mass = (% abundance of isotope 1)(mass of isotope 1) + (% abundance of isotope 2)(mass of isotope 2)
What happens during the decay of a radioisotope?
It spontaneously produces two or more smaller nuclei and radiation
What are noble gases known for?
They are stable and inert because they have a stable octet
How is the atomic mass expressed?
In decimals
Who proposed that all matter can be divided into smaller pieces until a single indivisible particle is reached?
Democritus
Democritus introduced the concept of the atom, meaning ‘cannot be cut’.
What are the three key characteristics of atoms proposed by Democritus?
- Atoms are of different sizes
- Atoms are in constant motion
- Atoms are separated by empty spaces
Which elements did Aristotle and Empedocles believe all matter was composed of?
- Earth
- Air
- Fire
- Water
What does Dalton’s theory state about atoms?
- Matter consists of definite particles called atoms
- Atoms cannot be created, destroyed, or divided
- Each element has its own type of atom
- Atoms of the same element have identical properties
- Atoms can combine in constant ratios to form new substances
What is the ‘Plum Pudding Model’ proposed by Thomson?
A model where positive and negative charges are evenly spread throughout the atom.
What was the main finding of Rutherford’s gold foil experiment?
The atom is mostly empty space with a tiny, dense nucleus.
What is the role of protons in an atom?
Protons determine the identity of the element.
What did Bohr’s experiments with hydrogen atoms reveal?
Electrons exist in specific energy levels and emit light when they transition between these levels.
What are isotopes?
Atoms with the same number of protons but a different number of neutrons.
Fill in the blank: Matter is anything that has mass and takes up _______.
space
What is the definition of an element?
A pure substance that cannot be broken down into simpler substances by any physical or chemical means.
What is a compound?
A pure substance composed of two or more different elements that are chemically joined.
What does IUPAC stand for?
International Union of Pure and Applied Chemistry
Who proposed using a code of letters as symbols for elements?
Jons Jakob Berzelius
True or False: Alchemy was a time of intense exploration of the nature of matter.
True
What is empirical knowledge?
Knowledge that comes from investigation and observation.
What is theoretical knowledge?
Knowledge that explains scientific observations.
Fill in the blank: A _______ is an explanation or model that depends on observation, experimentation, and reasoning.
theory
What are the two main types of knowledge in scientific research?
- Empirical Knowledge
- Theoretical Knowledge
What is the modern model used by physicists and chemists to describe electrons?
Quantum Mechanical Model
What is the significance of the periodic table?
Each element has its own square containing the element symbol, atomic number, and atomic mass.
What information is contained in each square of the periodic table?
Element symbol, atomic number, atomic mass
In what year were 31 elements known?
1800
Who proposed the law of triads?
Johann Dobereiner
What does the law of triads state?
The middle element has an atomic mass about halfway between the other two
What pattern did John Alexander Newlands observe?
Similar chemical and physical properties appeared for every 8th element
What is the law of octaves?
The observation that every 8th element has similar properties
Who published the first periodic law?
Dmitri Mendeleev
What did Mendeleev do with the elements in his periodic table?
Listed them in horizontal rows by atomic mass and grouped similar properties
What are the two main classifications of rows and columns in the periodic table?
Rows are called periods, and columns are called groups or chemical families
What do elements in the same group share?
Certain physical and chemical properties
What are the characteristics of Group 1 elements?
Soft, silver-coloured, very reactive metals with 1 valence electron
Fill in the blank: Group 2 elements are known as _______.
Alkaline Earth Metals
What are the properties of Group 17 elements?
May be solids, liquids, or gases; extremely reactive; 7 valence electrons
What are the characteristics of Noble Gases in Group 18?
Gases at SATP, extremely unreactive, full outer shell
What three classes can elements be divided into based on properties?
- Metals
- Non-Metals
- Metalloids
What are the characteristics of metals?
Most are solid at SATP, shiny, excellent conductors, malleable, ductile
How many non-metals are there, and what are their states at room temperature?
17 non-metals: 11 gases, 5 solids, 1 liquid
What are metalloids?
Elements with metallic and non-metallic properties, semi-conductors, brittle solids
What are Bohr-Rutherford diagrams used for?
To show the subatomic particles in an atom
What do chemical reactions involve in an atom?
Valence electrons in the valence shell
How many electrons can each orbital hold?
- Orbital #1: 2 electrons
- Orbital #2: 8 electrons
- Orbital #3: 8 electrons
What do Lewis Dot diagrams represent?
Valence electrons
How many valence electrons does Oxygen have?
6 valence electrons
What are lone pairs in the context of Lewis Dot diagrams?
Electrons that are by themselves
What is a trend in the context of the periodic table?
A predictable change in a particular direction
What happens to atomic radius as you move across a period?
Decreases
What is the atomic radius?
A measurement of the size of an atom, usually expressed in picometres (pm)
What causes the atomic radius to decrease across a period?
Increased nuclear charge with no additional shielding
What happens to atomic radius as you move down a group?
Increases
What is the effective nuclear charge (ENC)?
The charge felt by valence electrons after accounting for shielding electrons
What is the relationship between positive ions and atomic radius?
Positive ions have a smaller radius than the neutral atom from which they are formed
What is ionization energy?
The quantity of energy required to remove a single valence electron from an atom or ion in a gaseous state
How does ionization energy change across a period?
Tends to increase
How does ionization energy change down a group?
Tends to decrease
What is electron affinity?
The energy change that occurs when an electron is added to a neutral atom in a gaseous state
How does electron affinity change across a period?
Increases
How does electron affinity change down a group?
Decreases
What is electronegativity?
The ability of an atom or molecule to attract pairs of electrons in a chemical bond
Which element is the most electronegative?
Fluorine
Fill in the blank: The outermost electrons are lost when an atom forms a _______.
Positive ion or cation
Fill in the blank: The addition of an electron from an atom results in the formation of a _______.
Negative ion or anion
True or False: Electronegativity decreases as you move across a period.
False
What is the first ionization energy?
The amount of energy required to remove the most weakly held electron from a neutral atom
What is the second ionization energy?
The amount of energy required to remove a second electron from a positive ion
What role does electron shielding play in atomic structure?
It decreases the effective nuclear charge felt by outer electrons
How does the number of energy levels affect atomic radius?
More energy levels increase atomic radius due to increased shielding
What happens to the electron cloud when an atom gains an electron?
It increases, leading to greater electron-electron repulsion
What is a chemical bond?
Forces of attraction holding atoms or ions together.
What is an ionic compound?
A pure substance formed from a metal and a non-metal composed of oppositely charged ions.
What happens to sodium and chlorine when they form an ionic bond?
Sodium loses a valence electron to form a cation, and chlorine accepts the electron to form an anion.
What is a molecular compound?
A pure substance formed from two or more different non-metals sharing electrons.
What are the properties of ionic compounds?
• Solids at SATP
• High melting point
• Neutral compounds
• Electrolytes
What is the reason for the high melting point of ionic compounds?
Ions are held together by strong electrostatic forces (ionic bonds).
What is an electrolyte?
A substance that forms a solution that conducts electricity.
What is the structure of ionic compounds known as?
Crystal lattice.
What does the arrangement of cations and anions in an ionic compound explain?
Why these substances are hard and brittle.
What is the smallest repeating unit in an ionic crystal structure called?
Formula unit.
What is the formula unit of potassium sulfide (K2S)?
2:1 ratio of potassium ions to sulfide ion.
What is a stable octet?
A full shell of eight electrons in the outer energy level of an atom.
How do metal atoms in Groups 1, 2, or 3 achieve a stable octet?
By losing electrons to form cations.
How do non-metal atoms in Groups 15, 16, or 17 achieve a stable octet?
By gaining electrons to form anions.
What are electron dot diagrams or Lewis symbols?
A representation of an atom or ion, made up of the chemical symbol and dots indicating the number of electrons in the valence energy level.
True or False: Noble gases are reactive because they have a stable octet.
False.
Fill in the blank: The electrostatic force between the cation and anion holds these ions together, forming an _______.
ionic bond.
What is the significance of water molecules in ionic compounds?
They surround each ion and separate it from the crystal, allowing ions to move and carry electric charges.
What is a molecular compound?
A pure substance formed from two or more different non-metals
Examples include water (H2O) and carbon dioxide (CO2)
Define a molecular element.
A pure substance composed of molecules made up of two or more atoms of the same element
Examples include O2, N2, and Cl2.
What is a diatomic molecule?
A molecule consisting of two atoms of the same or different elements
What is a polyatomic molecule?
A molecule consisting of more than two atoms of the same or different elements
Define a covalent bond.
The bond that results from the sharing of a pair of electrons by two atoms
What is a coordinate covalent bond?
A covalent bond in which both of the shared electrons come from the same atom
What is bonding capacity?
The number of covalent bonds that an atom can form
What do Lewis symbols represent?
They represent the valence electrons surrounding each of the component atoms as dots
What is a Lewis structure?
A diagram that shows the valence electrons and the covalent bonds in a molecule
What is a structural formula?
A representation of the numbers, types, and arrangement of atoms in a molecule, with dashes representing covalent bonds
List the states of matter that molecular substances can exist in at SATP.
Gases, liquids, and solids
What are the typical boiling and melting points of molecular compounds?
Relatively low boiling points and melting points
Do many molecular substances dissolve readily in water?
No, many do not dissolve readily in water
What type of forces are intra-molecular forces?
Forces of attraction and repulsion within the compound
What are inter-molecular forces?
Forces of attraction and repulsion between the compound
True or False: Covalent bonds are weaker than inter-molecular forces.
False
What effect does the number of electron pairs in a bond have on bond strength?
The strength of the bond increases as the number of electron pairs in the bond increases
What is the IUPAC naming system used for?
Naming and identifying compounds
The International Union of Pure and Applied Chemistry (IUPAC) provides a systematic approach for naming chemical compounds.
Define binary ionic compounds.
A compound that consists of ions of only two elements
Examples include NaCl and MgO.
Define polyatomic ionic compounds.
A compound that consists of ions of more than two different elements
Examples include CaCO3 and HNO3.
What is the order of naming in ionic compounds?
Metal then non-metal
The non-metal typically has the suffix -ide.
What does the criss-cross method refer to in writing chemical formulas?
A method to determine the charges of ions and to write the chemical formula
Ensures subscripts are the lowest whole number ratio.
What should you do if there is a one in the subscript of a chemical formula?
You do NOT have to write it
Subscripts of ‘1’ are typically omitted in chemical formulas.
What is a multivalent metal?
A metal that can form a variety of cations, each with a different charge
Examples include Fe2+ and Fe3+.
How do you indicate the charge of a multivalent cation in a compound’s name?
By writing the appropriate Roman numeral in brackets following the name of the ion
Example: Iron (III) oxide.
What is the first step in naming ionic compounds with multivalent ions?
Recognize that the compound has an element that can have more than one charge
Example: Lead can be +2 or +4.
What is the purpose of the reverse criss-cross method?
To determine the charge on a multivalent cation
Used after recognizing the multivalent nature of the metal.
What is the naming convention for oxyanions with one more oxygen than the ‘–ate’ ion?
Add the prefix PER and the suffix -ATE
Example: ClO4- is called perchlorate.
What is the naming convention for oxyanions with one less oxygen than the ‘–ate’ ion?
Add the suffix -ITE
Example: ClO2- is called chlorite.
How do you name a hydrate?
Use prefixes to indicate the number of water molecules present
Example: CuSO4 • 5 H2O is named copper(II) sulfate pentahydrate.
Fill in the blank: A hydrate is an ionic compound that contains _______ as part of its crystal structure.
water
Hydrates include water molecules within their structure.
What is the chemical formula for calcium carbonate?
CaCO3
Calcium carbonate is a common polyatomic ionic compound.
What is the chemical formula for iron(III) hydroxide?
Fe(OH)3
Represents an ionic compound with a multivalent metal and a polyatomic ion.
True or False: The name of the compound NaCl is sodium chloride.
True
Sodium chloride is the standard name for this binary ionic compound.
What is electronegativity?
The ability of an individual atom, when bonded, to attract the bonding electrons to itself
Developed by Linus Pauling in 1922.
Who developed the concept of electronegativity?
Linus Pauling
Developed the concept in 1922.
Which element has the highest electronegativity?
Fluorine
Which element has the lowest electronegativity?
Francium
What does a high electronegativity indicate?
An atom is very good at pulling a pair of electrons toward itself.
Can electronegativity be measured experimentally?
No, it is calculated using physical properties such as ionization energy.
What is ΔEN?
The difference in electronegativities of two bonded atoms or ions.
What does a greater ΔEN indicate about a bond?
The more likely it is that the bond is ionic.
What type of bond is formed between two identical atoms?
Non-Polar Covalent Bond
What is the electronegativity difference (ΔEN) in a non-polar covalent bond?
ΔEN = 0
What characterizes a polar covalent bond?
Formed between two atoms with significantly different electronegativities resulting in localized charges.
What happens to the electrons in a polar covalent bond?
The more electronegative atom pulls the electrons closer, resulting in a partial negative charge.
What is the criterion for a bond to be classified as ionic?
ΔEN > 1.7
What is a polar molecule?
A molecule that is slightly positively charged at one end and slightly negatively charged at the other end due to electronegativity differences.
What is a key factor that can make a molecule non-polar despite having polar bonds?
Symmetry in 3D space.
What are the criteria for a compound to be considered polar?
- There are lone pairs of electrons on the central atom
- It is not symmetrical
- There is only one atom attached to the central atom
What determines the physical properties of a substance?
Intermolecular forces.
What are Van der Waals Forces?
Weak intermolecular attractions that include London Dispersion forces and Dipole-Dipole forces.
What causes London Dispersion Forces?
A temporary imbalance of electrons within entities.
What is a dipole-dipole force?
An intermolecular force of attraction between the slightly positive end of one polar molecule and the slightly negative end of an adjacent polar molecule.
What is a hydrogen bond?
An unusually strong dipole-dipole force between a hydrogen atom attached to a highly electronegative atom (N, O, or F).
What role do hydrogen bonds play in DNA?
Hold the two helixes of DNA together.
