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Classified in Chemistry

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2.1 Properties of Matter~Properties used to describe matter can be classified as extensive or intensive.~Every sample of a given substance has identical intensive properties because every sample has the same composition.~Three states of matter are solid, liquid, and gas.~Physical changes can be classified as reversible or irreversible. 2.2 Mixtures~Mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures, based on the distribution of their components.~Differences in physical properties can be used to separate mixtures.2.3 Elements and Compounds~Compounds can be broken down into simpler substances by chemical means, but elements cannot.~If the composition of a material is fixed, the material is a substance. If the composition may vary, the material is a mixture.~Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.2.4 Chemical Reactions~During a chemical change, the composition of matter always changes.~Four possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate.~During any chemical reaction, the mass of the products is always equal to the mass of the reactants.3.1 Measurements and Their Uncertainty~Measurements are fundamental to the experimental sciences.~To evaluate accuracy, the measured value must be compared to the correct value. To evaluate precision, you must compare the values of repeated measurements.~Calculated answers often depend on the number of significant figures in the values used in the calculation.~In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated.Hint3.2 The International System of Units~Five commonly used SI base units are the meter, kilogram, kelvin, second, and mole.~ length: cm, m, km. Volume: μL, mL, L, cm3. Common metric units of mass: mg, g, kg.Temperature: °C and K.  energy: J and cal.3.3 Conversion Problems~Multiplying by a conversion factor does not change the actual size of a measurement.~Dimensional analysis provides an alternative approach to problem solving.~Conversion problems are easily solved using dimensional analysis.3.4 Density~Density is an intensive property that depends only on the composition of a substance.~The density of a substance generally decreases as its temperature increases4.1 Defining the Atom~Democritus believed that atoms were indivisible and indestructible.~By using experimental methods, Dalton transformed Democritus's ideas on atoms into a scientific theory.~Scientists can observe individual atoms by using instruments such as scanning tunneling microscopes.4.2 Structure of the Nuclear Atom~Three types of subatomic particles are electrons, protons, and neutrons.~In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.4.3 Distinguishing Among Atoms~Elements are different because they have different numbers of protons.~The number of neutrons in an atom is the difference between the mass number and atomic number.~Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.~To calculate the atomic mass of an element, multiply the mass of each isotope by its natural percent abundance (expressed as a decimal), and then add the products.~The periodic table lets you easily compare the properties of one element (or a group of elements) to another element (or group of elements).5.1 Models of the Atom~Rutherford’s planetary model could not explain the chemical properties of elements.~Bohr proposed that electrons move only in specific circular paths, or orbits, around the nucleus.~The quantum mechanical model determines the allowed energies an electron can have and how likely it is to be found in various locations around the nucleus.~Each sublevel of a principal energy level corresponds to an orbital shape describing where the electron is likely to be found.5.2 Electron Arrangement in Atoms~Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms.~Some actual electron configurations differ from those assigned using the aufbau principle because half-filled levels are not as stable as filled levels, but they are more stable than other configurations.5.3 Physics and the Quantum Mechanical Model~The wavelength and frequency of light are inversely proportional to each other.~When atoms absorb energy, electrons move into higher energy levels, and then lose energy by emitting light when the electrons drop back to lower energy levels.~The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.~Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves.

6.1 Organizing the Elements~Chemists used the properties of elements to sort them into groups.~Mendeleev arranged the elements in his periodic table in order of increasing atomic mass.~In the modern periodic table, elements are arranged in order of increasing atomic number. The elements within a group in the table have similar properties.~Three classes of elements are metals, nonmetals, and metalloids.6.2 Classifying the Elements~The periodic table displays the symbols and names of elements, along with information on the structure of their atoms.~Elements can be sorted into noble gases, representative elements, transition metals, or inner transition metals based on their electron configurations.~The periodic table can be divided into s, p, d, and f blocks that correspond to the highest occupied sublevels in atoms of elements.6.3 Periodic Trends~In general, atomic size increases from top to bottom within a group and decreases from left to right across a period.~Positive and negative ions form when electrons are transferred between atoms.~First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.~Cations are always smaller than the atoms from which they form. Anions are always larger than the atoms from which they form.~In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.~Trends in atomic size, ionization energy, ionic size, and electronegativity can be explained by variations in atomic structure. The increase in nuclear charge within groups and across periods explains many trends. Within groups an increase in shielding has a significant effect.

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