General Chemistry Example 2.5

Questions and Answers

What did Thomson's experiments reveal about cathode rays?

They are identical regardless of the substance. (correct)

They are larger than atoms.

They have a positive charge.

They are composed of neutrons.

Which of the following statements is a key aspect of Dalton’s atomic theory?

Atoms are composed solely of empty space.

Atoms consist only of protons and electrons.

Atoms have varying charges based on substance.

Atoms cannot be created or destroyed. (correct)

What is the primary reason isotopes of an element have different masses?

They have different atomic numbers.

They have different numbers of protons.

They have different numbers of neutrons. (correct)

They have different numbers of electrons.

What is the primary function of neutrons in an atom?

To maintain the mass number. Signup and view all the answers

What does the mass number of an isotope represent?

The sum of protons and neutrons. Signup and view all the answers

What is the charge of an atom when it contains equal numbers of protons and electrons?

Neutrally charged Signup and view all the answers

In the isotopic symbol 14C, what does the number 14 represent?

The mass number of the carbon isotope. Signup and view all the answers

How many neutrons are present in the isotope 19F?

10 neutrons. Signup and view all the answers

Which statement best describes the atomic nucleus?

It holds almost all the mass of the atom. Signup and view all the answers

How many neutrons are indicated in the isotope symbol 238U?

146 neutrons. Signup and view all the answers

Which of the following isotopic symbols is correct?

12C Signup and view all the answers

What is the N:O mass ratio for nitrogen monoxide (NO)?

0.8756 Signup and view all the answers

Which element has isotopes represented by the symbols 1H and 2H?

Hydrogen. Signup and view all the answers

Which statement best describes the law of multiple proportions?

The mass ratios of elements in a compound yield whole numbers when compared. Signup and view all the answers

What is the number of protons, neutrons, and electrons in a neutral sulfur isotope represented as S-32?

16 p, 16 e, 16 n. Signup and view all the answers

What is the N:O mass ratio for nitrogen dioxide (NO2)?

0.4378 Signup and view all the answers

According to Dalton's atomic theory, what is true about atoms of different elements?

They have different masses. Signup and view all the answers

What can be concluded from the ratio of the N:O mass ratios of NO and NO2 being a whole number?

They follow the law of multiple proportions. Signup and view all the answers

What does the law of definite proportions state?

Elements combine in fixed ratios to form compounds. Signup and view all the answers

What type of particles are atoms made up of according to atomic theory?

Indivisible particles Signup and view all the answers

How do the masses of the oxygen atoms in NO and NO2 differ?

NO2 has a larger mass. Signup and view all the answers

Which of the following elements is classified as a metal?

Calcium, Ca Signup and view all the answers

What distinguishes metalloids from metals and nonmetals?

Metalloids share properties with both metals and nonmetals. Signup and view all the answers

Which element listed is a nonmetal?

Phosphorus, P Signup and view all the answers

What is the first alkaline earth metal in the periodic table?

Beryllium, Be Signup and view all the answers

Which of the following elements is located in the fourth period and belongs to group 6?

Cr Signup and view all the answers

Which of the following is the third halogen in the periodic table?

Bromine, Br Signup and view all the answers

What is the fifth element in the first row of transition metals?

Mn Signup and view all the answers

Which of the following metals is classified as a coinage metal?

Copper, Cu Signup and view all the answers

What is the primary criterion for the arrangement of elements in the modern periodic table?

Increasing atomic number Signup and view all the answers

Who were the two scientists known for their significant contributions to the development of the periodic table?

Dmitri Mendeleev and Lothar Meyer Signup and view all the answers

What unique approach did Mendeleev take in organizing the periodic table?

He arranged elements by similar properties regardless of atomic mass. Signup and view all the answers

Which of the following statements is true regarding Mendeleev's predictions?

He accurately predicted the properties of several undiscovered elements. Signup and view all the answers

How does the modern periodic table differ from earlier versions?

It arranges elements by atomic number instead of atomic mass. Signup and view all the answers

Which pair of elements besides iodine (I) and tellurium (Te) is known to be out of order based on atomic masses?

Arsenic (As) and Selenium (Se) Signup and view all the answers

What was the main method used by early scientists to determine the arrangement of elements before Mendeleev's contributions?

Arrange them by increasing atomic masses. Signup and view all the answers

What critical assumption did Mendeleev make about the atomic masses of certain elements?

Misidentified masses could reflect atomic similarities. Signup and view all the answers

Study Notes

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.

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Description

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.