Introduction to Chemistry: Exam 1 Study Guide

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Ch. 1 The Chemical World

The Scientific Method

The scientific method is a systematic approach used in scientific study to investigate phenomena, acquire new knowledge, or correct and integrate previous knowledge. It is fundamental to all scientific disciplines, including chemistry.

Observation: Gathering data and noticing phenomena.
Hypothesis: A tentative explanation or prediction that can be tested.
Experimentation: Testing the hypothesis through controlled experiments.
Analysis: Interpreting data to draw conclusions.
Theory: A well-substantiated explanation based on repeated experiments.

Example: Observing that iron rusts in the presence of water and air, hypothesizing that oxygen is required for rusting, and designing experiments to test this hypothesis.

Ch. 2 Measurements & Problem Solving

Scientific Notation

Scientific notation expresses numbers as a product of a coefficient and a power of ten, making it easier to handle very large or small values.

General form: where and is an integer.
Example:

Significant Figures and Rounding

Significant figures are the digits in a measurement that are known with certainty plus one estimated digit. They reflect the precision of a measurement.

Rules for identifying significant figures:
- All nonzero digits are significant.
- Zeros between nonzero digits are significant.
- Leading zeros are not significant.
- Trailing zeros are significant only if there is a decimal point.
When rounding, retain only as many significant figures as justified by the measurement or calculation.

SI Prefix Multipliers (Table 2.2)

SI prefixes are used to express multiples or fractions of base units in the metric system.

Prefix	Symbol	Multiplier
kilo-	k
centi-	c
milli-	m
micro-	\mu
nano-	n
mega-	M

Multistep Conversions

Many chemistry problems require converting between units using conversion factors. Multistep conversions involve using more than one conversion factor in sequence.

Set up the problem so that units cancel appropriately.
Example: Converting 5.0 km to cm:

Ch. 3 Matter & Energy

Classification of Matter by Composition

Matter can be classified based on its composition as elements, compounds, or mixtures.

Element: A pure substance made of only one kind of atom (e.g., O2).
Compound: A substance composed of two or more elements chemically combined (e.g., H2O).
Mixture: A physical blend of two or more substances (e.g., air, saltwater).

Physical and Chemical Properties

Physical properties: Can be observed without changing the substance’s identity (e.g., melting point, density).
Chemical properties: Describe a substance’s ability to undergo chemical changes (e.g., flammability, reactivity).

Conservation of Mass

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.

Mass of reactants = Mass of products
Example: Burning 10 g of hydrogen with 80 g of oxygen produces 90 g of water.

Energy and Heat Capacity Calculations

Energy is the capacity to do work or produce heat. Heat capacity is the amount of heat required to raise the temperature of a substance by 1°C.

Specific heat capacity (): Amount of heat needed to raise 1 g of a substance by 1°C.
Formula:
Where = heat (J), = mass (g), = specific heat (J/g°C), = change in temperature (°C).

Ch. 4 Atoms & Elements

Elements: Defined by Their Numbers of Protons

Atomic number (Z): Number of protons in the nucleus; defines the element.
Atomic symbol: One- or two-letter abbreviation for an element (e.g., H for hydrogen).
Element name: The full name of the element (e.g., Carbon).

Looking for Patterns: The Periodic Law and the Periodic Table

The periodic law states that the properties of elements recur periodically when arranged by increasing atomic number. The periodic table organizes elements into periods (rows) and groups (columns) based on similar properties.

Metals, nonmetals, and metalloids are classified based on their properties.
Groups/families have similar chemical behaviors (e.g., alkali metals, halogens).

Ions: Losing and Gaining Electrons

Cation: Positively charged ion formed by losing electrons (e.g., Na+).
Anion: Negatively charged ion formed by gaining electrons (e.g., Cl-).
Example: Sodium atom loses one electron to become Na+.

Isotopes

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

Notation: , where = mass number, = atomic number, = element symbol.
Example: and are isotopes of carbon.

Ch. 9 Electrons in Atoms & The Periodic Table

Quantum-Mechanical Orbitals, Electron Configurations, and Orbital Diagrams

Electrons in atoms occupy quantum-mechanical orbitals, which are regions of space where there is a high probability of finding an electron.

Electron configuration: The arrangement of electrons in an atom’s orbitals.
Orbital diagram: A pictorial representation showing electrons as arrows in boxes representing orbitals.
Aufbau principle, Pauli exclusion principle, and Hund’s rule govern electron filling order.

Electron Configurations and the Periodic Table

The periodic table reflects the recurring pattern of electron configurations. Elements in the same group have similar valence electron configurations, leading to similar chemical properties.

Example: All alkali metals have a single electron in their outermost s orbital.

Periodic Trends: Atomic Size, Ionization Energy, and Metallic Character

Certain properties of elements change in predictable ways across periods and down groups in the periodic table.

Trend	Across a Period (Left to Right)	Down a Group
Atomic Size	Decreases	Increases
Ionization Energy	Increases	Decreases
Metallic Character	Decreases	Increases

Atomic size: Distance from nucleus to outermost electron.
Ionization energy: Energy required to remove an electron from an atom.
Metallic character: Tendency to lose electrons and exhibit properties of metals.