General Chemistry Example 2.5

Law of Multiple Proportions

• Nitrogen monoxide (NO) consists of 14.01 g of nitrogen and 16.00 g of oxygen, yielding an N:O ratio of approximately 0.8756.
• Nitrogen dioxide (NO2) contains 14.01 g of nitrogen and 32.00 g of oxygen, giving an N:O ratio of approximately 0.4378.
• Dividing the larger ratio (0.8756) by the smaller ratio (0.4378) results in a ratio of 2.000, confirming the law of multiple proportions.

Laws of Chemical Composition

• Three fundamental laws guide chemical reactions: conservation of mass, definite proportions, and multiple proportions.
• These laws were established through careful measurements of reactants and products in chemical processes, forming the foundation of modern chemistry.

Dalton's Atomic Theory

• Matter is composed of tiny, indivisible particles called atoms.
• Atoms of the same element share identical mass; atoms of different elements have distinct masses.
• Isotopes are variations of elements with the same atomic number but different neutron counts, identified by their mass number (A).

Mass Number and Isotopes

• Mass number (A) is the sum of protons (p) and neutrons (n): A = Z + n, where Z is the atomic number.
• The number of neutrons is calculated as n = A - Z.
• Isotopes are labeled utilizing the element's name or symbol followed by the mass number (e.g., hydrogen-1 as ¹H and hydrogen-2 as ²H).

Counting Subatomic Particles

• For S-32: 16 protons, 16 electrons, 16 neutrons.
• For ¹⁹F: 9 protons, 9 electrons, 10 neutrons.
• A neon atom with equal protons and neutrons contains 10 protons, 10 electrons, and 10 neutrons.
• For ²⁳⁵U: 92 protons, 92 electrons, and 146 neutrons.

Characteristics of Elements

• Metals, located on the left of the periodic table, are shiny, malleable, ductile, and good conductors.
• Nonmetals are predominantly found on the upper right side and are often brittle.
• Metalloids have properties that are intermediate between metals and nonmetals.

Periodic Table Development

• The modern periodic table organizes elements by increasing atomic number and grouped by similar properties.
• Initially arranged by atomic mass, the table was refined over time.
• Dimitri Mendeleev and Lothar Meyer were instrumental in developing the periodic table, with Mendeleev predicting the properties of undiscovered elements.

Out of Order Elements

• Mendeleev's table had iodine (I) and tellurium (Te) placed contrary to their atomic masses but based on chemical properties.
• Elements can occasionally be out of order; other instances include pairs that also show similar properties rather than atomic mass.

Subatomic Particles Overview

• Subatomic particles include neutrons, protons, and electrons, with the nucleus being significantly small.
• The nucleus accounts for nearly all atomic mass, while electrons occupy most of the atomic volume.
• Atoms maintain electrical neutrality by having an equal number of protons and electrons.

Explore the concept of multiple proportions through an example comparing nitrogen monoxide (NO) and nitrogen dioxide (NO2). Calculate the nitrogen to oxygen ratio for both compounds to demonstrate their relationship as per the law of multiple proportions.