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Periodic Table and Element Classification

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Termini in questo insieme (104)

  • What defines an element's position in the periodic table?
    An element's position is defined by its atomic number, which is the number of protons in its nucleus.
  • What are alkali metals and where are they located on the periodic table?
    Alkali metals are highly reactive metals found in Group 1 of the periodic table, excluding hydrogen.
  • Which group contains the noble gases and what is their characteristic?
    Noble gases are in Group 18 and are characterized by their inertness due to a full valence electron shell.
  • What are transition metals and where are they found?
    Transition metals are elements in the d-block (Groups 3-12) known for variable oxidation states and forming colored compounds.
  • What distinguishes halogens on the periodic table?
    Halogens are in Group 17 and are highly reactive nonmetals with seven valence electrons.
  • What are lanthanides and actinides?
    Lanthanides and actinides are the f-block elements, often shown below the main table, with lanthanides being rare earth metals and actinides mostly radioactive.
  • How are elements classified by their metallic character?
    Elements are classified as metals, nonmetals, or metalloids based on properties like conductivity, malleability, and appearance.
  • What is the significance of atomic weight in the periodic table?
    Atomic weight represents the average mass of an element's isotopes weighted by abundance.
  • What is the general trend of atomic radius across a period?
    Atomic radius generally decreases from left to right across a period due to increasing nuclear charge.
  • What is the general trend of atomic radius down a group?
    Atomic radius generally increases down a group because of added electron shells.
  • What is the relationship between group number and valence electrons in main group elements?
    The group number corresponds to the number of valence electrons in main group elements.
  • Which elements are considered noble gases?
    Noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
  • What is the significance of the periodic table's group and period structure?
    Groups are vertical columns with elements sharing similar chemical properties; periods are horizontal rows indicating increasing atomic number.
  • What are metalloids and where are they located?
    Metalloids have properties between metals and nonmetals and are found along the stair-step line between metals and nonmetals.
  • What is the difference between main group elements and transition metals?
    Main group elements are in groups 1, 2, and 13-18 with predictable valence electrons; transition metals are in groups 3-12 with variable oxidation states.
  • What elements are included in the alkaline earth metals group?
    Alkaline earth metals are in Group 2 and include beryllium, magnesium, calcium, strontium, barium, and radium.
  • How are rare-earth elements categorized?
    Rare-earth elements include the lanthanides and sometimes scandium and yttrium, known for their similar properties.
  • What is the significance of the actinide series?
    The actinide series contains mostly radioactive elements, many of which are synthetic and used in nuclear applications.
  • What is the general trend of electronegativity across a period?
    Electronegativity generally increases from left to right across a period.
  • What is the general trend of electronegativity down a group?
    Electronegativity generally decreases down a group due to increasing atomic radius.

  • Atoms

    The smallest unit of an element that retains its chemical identity

  • Molecules

    Two or more atoms bonded together; the properties of molecules depend on both the types of atoms and their arrangement.

  • Hypothesis

    A tentative explanation for an observation, which can be tested by experiments.

  • Scientific Law

    A statement that summarizes a vast number of experimental observations and describes what happens.

  • Theory

    A well-substantiated explanation of some aspect of the natural world; explains why phenomena occur.

  • Pure substances

    Have a fixed composition; can be elements or compounds.

  • Elements

    Consists of only one type of atom (e.g., O2).

  • Compounds

    Consist of two or more elements chemically combined (e.g., H2O).

  • Mixtures

    Physical combinations of two or more substances.

  • Heterogeneous Mixture:

    Composition varies throughout (e.g., salad).

  • Homogeneous Mixture (Solution):

    Uniform composition (e.g., saltwater)

  • States of Matter

    Solid, liquid, gas

  • Solid

    Definite shape and volume; particles are closely packed.

  • Liquid

    Definite volume, no definite shape; particles can move past each other.

  • Gas

    No definite shape or volume; particles are far apart and move freely.

  • Crystalline:

    Atoms/molecules arranged in a repeating pattern (e.g., salt).

  • Amorphous:

    No long-range order (e.g., glass).

  • Decanting:

    Pouring off a liquid from a solid-liquid mixture.

  • Distillation:

    Separating substances based on differences in boiling points

  • Filtration:

    Separating solids from liquids using a porous barrier.

  • Physical Properties:

    Can be observed without changing the substance (e.g., color, melting point).

  • Chemical Properties:

    Describe a substance's ability to undergo chemical changes (e.g., flammability)

  • Physical Change:

    Alters appearance, not composition (e.g., melting ice).

  • Chemical Change:

    Alters composition (e.g., rusting iron).

  • Work

    The action of a force through a distance.

  • Energy

    The capacity to do work

  • Kinetic Energy

    Energy of motion

  • Potential Energy:

    Energy due to position or composition.

  • Thermal Energy:

    Energy associated with temperature.

  • SI Units

    Standard units for scientific measurement.

    Length: meter (m)

    Mass: kilogram (kg)

    Time: second (s)

    Temperature: kelvin (K)

    Amount: mole (mol)

    Electric current: ampere (A)

    Luminous intensity: candela (cd)

  • Derived Units

    Volume (m3), Density (kg/m3).

  • Intensive Properties

    Independent of amount (e.g., density, temperature).

  • Extensive Properties

    Depend on amount (e.g., mass, volume)

  • Measurement Uncertainty:

    All measurements have some degree of uncertainty.

  • Significant Figures

    Digits that reflect the precision of a measurement.

    Nonzero digits are always significant

    Zeros between nonzero digits are significant

    Leading zeros are not significant

    Trailing zeros after a decimal are significant

  • Exact Numbers

    Have infinite significant figures (e.g., defined quantities).

  • Accuracy:

    How close a measurement is to the true value.

  • Precision:

    How close repeated measurements are to each other.

  • Brownian Motion

    The random movement of particles suspended in a fluid, observed by Robert Brown and explained by Einstein as resulting from collisions with moving molecules. This provided evidence for the particulate nature of matter.

  • Early Atomic Theory

    Leucippus & Democritus:

    Proposed matter is made of indivisible atoms

  • Early Atomic Theory

    Aristotle & Plato:

    Believed matter could be divided infinitely

  • Law of Conservation of Mass:

    Matter is not created or destroyed in chemical reactions

  • Law of Definite Proportions

    Compounds have elements in fixed ratios

  • Law of Multiple Proportions:

    Elements combine in small whole-number ratios to form different compounds

  • Dalton's Atomic Theory

    1. Elements are composed of atoms.

    2. Atoms of the same element are identical; atoms of different elements are different.

    3. Atoms combine in simple whole-number ratios to form compounds.

    4. Atoms are rearranged in chemical reactions, not created or destroyed

  • Protons

    Positively charged particles in the nucleus(+1)

    Protons determine the element's identity.

  • Neutrons

    Neutral particles in the nucleus(0)

  • Electrons

    Negatively charged particles outside the nucleus(-1)

  • Cathode Ray Experiment:

    J.J. Thomson discovered the electron.

  • Millikan's Oil Drop Experiment

    Measured the charge of the electron.

  • Plum Pudding Model:

    Thomson's model of the atom as a sphere of positive charge with embedded electrons.

  • Rutherford's Gold Foil Experiment:

    Showed that atoms have a small, dense, positively charged nucleus

  • Nuclear Theory:

    Most of the atom's mass and all of its positive charge are in the nucleus; electrons occupy most of the atom's volume.

  • Atomic Number:

    Number of protons

  • Mass Number:

    Protons + Neutrons

  • Neutrons

    Mass Number - Protons

  • Isotopes

    are atoms of the same element with different numbers of neutrons (and thus different mass numbers).

  • Cation

    Positive ion (loses electrons, e.g., Na → Na+)

  • Anion

    Negative ion (gains electrons, e.g., Cl + e- → Cl-)

  • Group 1 (Alkali Metals):

    1 valence electron, form +1 ions

  • Group 2 (Alkaline Earth Metals):

    2 valence electrons, form +2 ions

  • Group 17 (Halogens):

    7 valence electrons, form -1 ions

  • Group 18 (Noble Gases):

    Full outer shell, unreactive

  • Periodic Table

    Metals: Left side of the periodic table, tend to lose electrons

    Nonmetals: Right side, tend to gain or share electrons

    Transition Metals: Middle of the periodic table

  • Atomic Mass

    Average mass of an element's isotopes (amu)

  • Molar Mass

    Mass of one mole of a substance (g/mol)

  • Mass Spectrometry:

    Technique to determine the masses and relative abundances of isotopes

  • Mole (mol)

    Amount of substance containing 6.022x10^23 particles (Avogadro's number).

    1 mole = 6.022x10^23

  • Mole Conversions

    Grams to Moles: grams ÷ molar mass = moles

    Moles to Grams: moles × molar mass = grams

    Moles to Particles: moles × 6.022 ×10^23

    Particles to Moles: particles /6.022×10^23

  • Ionic Bond:

    Metal + Nonmetal; electrons are transferred (e.g., NaCl)

  • Covalent Bond:

    Nonmetal + Nonmetal; electrons are shared (e.g., H2O)

  • Ionic Compound:

    Contains ions (e.g., NaCl); the smallest unit is a formula unit

  • Molecular Compound:

    Atoms connected by covalent bonds (e.g., CO2); the smallest unit is a molecule

    -Use prefixes to indicate number of atoms (e.g., CO2: carbon dioxide)

  • Molecular Elements

    Some elements exist naturally as molecules, especially the seven diatomic elements: H2, N2, F2, O2, I2, Cl2, Br2.

    Memory trick: Have No Fear Of Ice Cold Beer

  • Empirical Formula

    Simplest whole-number ratio (e.g., CH2O)

  • Molecular Formula

    Actual number of atoms in a molecule (e.g., C6H12O6)

  • Structural Formula

    Shows how atoms are connected (e.g., H–O–H for water).

  • Formula Mass: Sum of atomic masses in a chemical formula.

    1. Find atomic mass of each element

    2. Multiply by number of atoms

    3. Add together

    Example: H2O: (2 × 1.01) + 16.00 = 18.02 g/mo

  • Mass percent is the percentage of a compound's mass from one element:

    Mass % = (mass of element in compound/total mass of compound) × 100

    Example: If oxygen is 16 g in a 20 g compound: 16/20 x 100 = 80%

  • Finding an Empirical Formula

    1. Convert grams to moles

    2. Divide by the smallest number of moles

    3. Get whole numbers

    4. Write the empirical formula

    Example: C = 1 mol, H = 2 mol, O = 1 mol → CH2O

  • Combustion analysis

    determines the formula of a compound by burning it and measuring the amounts of CO2 and H2O produced. This allows calculation of the empirical formula using mole ratios.

  • Metric Prefixes

    Giga(G) = 10^9

    Mega(M) = 10^6

    Kilo(k) = 10^3

    Deci(d) = 10^-1

    Centi(c) = 10^-2

    Micro(u) = 10^-6

    Nano(n) = 10^-9

    Pico(p) = 10^-12

  • Formulas

    D = m/V

    m = DxV

    V = m/D

  • Molecular Compounds

    1- mono

    2 -di

    3 -tri

    4 -tetra

    5 -penta

    6 -hexa

    7 -hepta

    8 -octa

    9 -nona

    10 -deca