General Chemistry Fundamentals: Measurement, Atomic Structure, and the Periodic Table

Chemistry Fundamentals

Introduction and Course Overview

This unit introduces foundational concepts in general chemistry, including laboratory safety, measurement, significant figures, dimensional analysis, atomic structure, and the periodic table. Mastery of these topics is essential for success in all areas of chemistry.

Measurement in Chemistry

Accuracy vs. Precision

Understanding the difference between accuracy and precision is crucial for evaluating experimental data.

• Accuracy: How close a measurement is to the accepted (true) value.

• Precision: How repeatable measurements are, regardless of their closeness to the true value.

• Data Repeatability: Precision is related to the consistency of repeated measurements.

• Instrumental Precision: Determined by the number of decimal places an instrument can record.

Example: Measuring the boiling point of water at 98.5°C, 101.2°C, and 100.0°C demonstrates varying degrees of accuracy and precision.

Lab Equipment

Proper use of laboratory equipment is essential for accurate measurements.

• Graduated Cylinder: Used for measuring liquid volumes accurately.

• Beaker: Used for holding and mixing chemicals; not for precise measurements.

• Erlenmeyer Flask: Used for mixing and heating chemicals; not for precise volume measurements.

• Buret: Used for dispensing precise volumes of liquids, especially in titrations.

Example: Reading the meniscus at eye level ensures accurate volume measurement.

Significant Figures

Significant figures (sig figs) indicate the precision of a measured value.

• Nonzero digits are always significant.

• Leading zeros are never significant.

• Captive (sandwiched) zeros are always significant.

• Trailing zeros are significant only if there is a decimal point.

Counting Significant Figures:

• 0.00782 has 3 sig figs.

• 1200 has 2 sig figs (unless specified otherwise).

• 2.68 x 103 has 3 sig figs.

Rounding: Round to the least number of significant figures in the calculation.

Adding/Subtracting: The answer should have the same number of decimal places as the measurement with the fewest decimal places.

Multiplying/Dividing: The answer should have the same number of significant figures as the measurement with the fewest significant figures.

Scientific Notation

Scientific notation is used to express very large or very small numbers conveniently.

• Positive exponent: Value is greater than 1 (e.g., $4.5 \times 10^3$).

• Negative exponent: Value is less than 1 (e.g., $6.77 \times 10^{-2}$).

Example: 43,900 in scientific notation is $4.39 \times 10^4$.

Density

Density is a physical property defined as mass per unit volume.

• Formula: $D = \frac{\text{Mass}}{\text{Volume}}$

• Units: g/mL or g/cm3 for liquids and solids; g/L for gases.

• Density is an intensive property (does not depend on the amount of substance).

Example: If a substance has a mass of 35.2 g and a density of 1.60 g/mL, its volume is:

$\text{Volume} = \frac{35.2\ \text{g}}{1.60\ \text{g/mL}} = 22.0\ \text{mL}$

Substance	Density (g/mL) at 25°C
Mercury	13.6
Water	1.00
Hexane (non-polar)	0.660
Ethyl Alcohol (polar)	0.789
Dichloromethane (polar)	1.33
Aluminum	2.70
Bromine (non-polar)	2.928
Gold	19.3

Additional info: This table is used to identify unknown liquids based on density.

Dimensional Analysis

Dimensional analysis is a method for converting between units using conversion factors.

• Always start with what you are given.

• Choose appropriate conversion factors.

• Ensure units cancel diagonally.

• Continue until the desired unit is reached.

Example: To convert 24 km/hr to m/s:

$24\ \text{km/hr} \times \frac{1000\ \text{m}}{1\ \text{km}} \times \frac{1\ \text{hr}}{3600\ \text{s}} = 6.67\ \text{m/s}$

Unit Symbols	Unit Conversions	Metric Prefixes
m, s, g, mol, K, L, atm, J, etc.	1 atm = 101.3 kPa 1 L = 1000 mL 1 m = 100 cm	kilo (k) = 103 centi (c) = 10-2 milli (m) = 10-3 micro (μ) = 10-6

Atomic Structure

Subatomic Particles

Atoms are composed of three main subatomic particles:

Particle	Symbol	Charge	Location
Proton	p+	+1	Nucleus
Neutron	n0	0	Nucleus
Electron	e-	-1	Electron cloud

• Protons define the atomic number and identity of the element.

• Neutrons contribute to the mass number but do not affect the element's identity.

• Electrons determine the atom's charge and chemical behavior.

Example: The nuclear symbol for an atom is written as:

$\prescript{A}{Z}{\text{X}}^{\text{charge}}$

Where A = mass number, Z = atomic number, X = element symbol.

Isotopes

Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons.

• Isotopes have the same atomic number but different mass numbers.

• Example: $\prescript{19}{9}{\text{F}}$ and $\prescript{20}{9}{\text{F}}$ are isotopes of fluorine.

Isotopic Notation	Protons	Neutrons	Electrons
$\prescript{27}{12}{\text{Mg}}$	12	15	12
$\prescript{36}{17}{\text{Cl}}^-$	17	19	18
$\prescript{19}{9}{\text{F}}$	9	10	9

The Periodic Table

Organization of the Periodic Table

The periodic table arranges elements by increasing atomic number and groups elements with similar properties into columns (groups or families) and rows (periods).

• Groups: Vertical columns; elements in the same group have similar chemical properties and the same number of valence electrons.

• Periods: Horizontal rows; elements in the same period have the same number of electron shells.

• Metalloids: Elements with properties intermediate between metals and nonmetals, typically found along the staircase line.

Valence Electrons and Ions

Valence electrons are the outermost electrons and determine an element's chemical reactivity.

Element	Group	# Valence Electrons	Charge in Ionic Compounds	Cation or Anion?
Rb	1	1	+1	Cation
N	15	5	-3	Anion
Ne	18	8	0	Neither
Mg	2	2	+2	Cation
Fe	8	2	+2, +3	Cation
F	17	7	-1	Anion

Lewis Dot Structures

Lewis dot structures represent valence electrons as dots around the element symbol. They are useful for predicting bonding and ion formation.

• Example: Calcium (Ca) as a neutral atom: Ca with two dots. As a Ca2+ ion: no dots.

• Example: Nitrogen (N) as a neutral atom: N with five dots. As an N3- ion: eight dots.

Summary Table: Key Concepts

Concept	Definition	Example
Accuracy	Closeness to true value	Measuring 100.0°C for boiling point of water
Precision	Repeatability of measurements	Measuring 99.9°C, 100.0°C, 100.1°C repeatedly
Significant Figures	Digits that reflect measurement precision	2.68 (3 sig figs)
Density	Mass per unit volume	$D = \frac{m}{V}$
Isotope	Same element, different neutrons	$\prescript{13}{6}{\text{C}}$ and $\prescript{14}{6}{\text{C}}$

Additional info: These notes provide a comprehensive overview of the foundational concepts in general chemistry, suitable for exam preparation and further study.