chapter three: periodic properties of the elements

Why is aluminum useful for airplane construction?

Aluminum has a relatively low density, so it provides a lot of material without adding as much mass as a denser metal.

What is density?

Density is the amount of mass contained in a certain volume. Density = mass ÷ volume.

What does a high density mean?

A high density means a large amount of mass is packed into a relatively small volume.

What does a low density mean?

A low density means less mass is packed into a given volume.

What does it mean when a property is a periodic property?

It means the property shows a repeating pattern when the elements are arranged by atomic number.

What causes periodic properties?

Periodic properties come from repeating patterns in the electron configurations of elements.

What happens to atomic number as you move across the periodic table?

Atomic number increases from left to right.

What is a periodic trend?

A periodic trend is a predictable pattern in a chemical or physical property as you move across or down the periodic table.

Why do properties repeat in the periodic table?

Properties repeat because elements periodically have similar valence-electron arrangements.

How did early scientists try to organize the elements?

They looked for repeating patterns in properties and atomic masses.

What was Döbereiner's contribution to the periodic table?

He identified groups of three elements called triads whose properties and atomic masses showed patterns.

What was Newlands' Law of Octaves?

Newlands proposed that when elements were arranged by increasing atomic mass, similar properties appeared approximately every eighth element.

What was a major problem with Newlands' arrangement?

It did not work well for all known elements and left no room for elements that had not yet been discovered.

What did Mendeleev do?

Mendeleev arranged elements mainly by increasing atomic mass while grouping elements with similar chemical properties together.

Why was Mendeleev's periodic table important?

He recognized repeating chemical patterns and left gaps for elements that had not yet been discovered.

Why did Mendeleev leave gaps in his table?

He believed undiscovered elements belonged in those positions based on the repeating patterns of properties.

What made Mendeleev's predictions impressive?

He predicted properties of several undiscovered elements, and later discoveries matched many of those predictions.

What did Lothar Meyer contribute?

Meyer independently recognized periodic relationships between atomic mass and properties of the elements.

What did Moseley discover?

Moseley showed that elements should be arranged by increasing atomic number rather than atomic mass.

What is the modern periodic law?

The physical and chemical properties of the elements are periodic functions of their atomic numbers.

Why is atomic number a better organizing principle than atomic mass?

Atomic number directly identifies the element and produces the correct repeating pattern of electron configurations and properties.

What is Coulomb's law about?

Coulomb's law describes the attraction or repulsion between charged particles.

What happens to the attraction between opposite charges when their distance increases?

The attraction becomes weaker as distance increases.

What happens to the attraction between opposite charges when their distance decreases?

The attraction becomes stronger.

How does nuclear charge affect an electron?

A more positively charged nucleus attracts an electron more strongly, all else being equal.

What is shielding?

Shielding occurs when electrons closer to the nucleus reduce the attraction that outer electrons feel toward the nucleus.

What causes shielding?

Inner electrons partially block the attraction between the positively charged nucleus and outer electrons.

What is effective nuclear charge, or Z_eff?

Effective nuclear charge is the net positive attraction an electron experiences from the nucleus after accounting for shielding.

What happens to effective nuclear charge across a period?

Z_eff generally increases from left to right because the number of protons increases while shielding does not increase by as much.

What is penetration?

Penetration describes how close an electron in an orbital can get to the nucleus.

Which type of orbital penetrates closest to the nucleus: s, p, d, or f?

s orbitals have the greatest penetration, followed by p, then d, then f.

Why does penetration matter?

Greater penetration allows an electron to experience a stronger attraction to the nucleus and affects orbital energy.

What is a quantum number?

A quantum number is a number used to describe a particular aspect of an electron's state in an atom.

What does the principal quantum number n describe?

n describes the main energy level or shell of an electron.

What values can n have?

n can be positive whole numbers: 1, 2, 3, 4, and so on.

What does the angular momentum quantum number l describe?

l describes the subshell and orbital shape.

What values can l have for a given n?

l can range from 0 to n − 1.

What does l = 0 represent?

l = 0 represents an s subshell.

What does l = 1 represent?

l = 1 represents a p subshell.

What does l = 2 represent?

l = 2 represents a d subshell.

What does l = 3 represent?

l = 3 represents an f subshell.

What does the magnetic quantum number m_l describe?

m_l describes the orientation of an orbital within a subshell.

What values can m_l have?

m_l ranges from −l through 0 to +l.

How many orbitals are in an s subshell?

An s subshell contains 1 orbital.

How many orbitals are in a p subshell?

A p subshell contains 3 orbitals.

How many orbitals are in a d subshell?

A d subshell contains 5 orbitals.

How many orbitals are in an f subshell?

An f subshell contains 7 orbitals.

How many electrons can one orbital hold?

One orbital can hold a maximum of 2 electrons.

How many electrons can an s subshell hold?

An s subshell can hold 2 electrons.

How many electrons can a p subshell hold?

A p subshell can hold 6 electrons.

How many electrons can a d subshell hold?

A d subshell can hold 10 electrons.

How many electrons can an f subshell hold?

An f subshell can hold 14 electrons.

What is the spin quantum number?

The spin quantum number describes the spin state of an electron and has two possible values.

What are the two possible electron spin values?

+1/2 and −1/2.

What is an orbital?

An orbital is a region of space where there is a high probability of finding an electron.

Is an orbital the same thing as an orbit?

No. An orbital is a probability region, not a fixed path around the nucleus.

What is the shape of an s orbital?

An s orbital is spherical.

What is the general shape of a p orbital?

A p orbital has two lobes and is often drawn like a dumbbell.

How many p orbitals are there in each p subshell?

There are three p orbitals.

What are the three p orbitals commonly called?

p_x, p_y, and p_z.

What is the general shape of d orbitals?

Most d orbitals have four-lobed shapes, although one has a different shape involving a ring and two lobes.

Why are there five d orbitals?

The allowed values of m_l for l = 2 give five possible orbital orientations.

Why are there seven f orbitals?

The allowed values of m_l for l = 3 give seven possible orbital orientations.

What is the Pauli exclusion principle?

No two electrons in an atom can have the exact same set of four quantum numbers.

What does the Pauli exclusion principle mean for an orbital?

An orbital can contain at most two electrons, and if two are present, they must have opposite spins.

What is Hund's rule?

When electrons occupy orbitals of equal energy, they occupy separate orbitals with parallel spins before pairing.

Why does Hund's rule matter?

It gives the lowest-energy arrangement for electrons in equivalent orbitals.

What is the Aufbau principle?

Electrons fill lower-energy orbitals before higher-energy orbitals.

What is an electron configuration?

An electron configuration shows how an atom's electrons are distributed among its orbitals.

What does 1s² mean?

It means the 1s orbital contains two electrons.

What does the superscript in an electron configuration tell you?

The superscript tells you how many electrons are in that subshell.

What does the number before a subshell letter mean?

It identifies the principal energy level.

What does the letter in an electron configuration represent?

It identifies the type of subshell: s, p, d, or f.

What is the general orbital filling order?

Electrons fill orbitals from lower to higher energy according to the established orbital-energy ordering.

What is the electron configuration of hydrogen?

1s¹

What is the electron configuration of helium?

1s²

What is the electron configuration of lithium?

1s² 2s¹

What is the electron configuration of carbon?

1s² 2s² 2p²

What is the electron configuration of nitrogen?

1s² 2s² 2p³

What is the electron configuration of oxygen?

1s² 2s² 2p⁴

What is the electron configuration of fluorine?

1s² 2s² 2p⁵

What is the electron configuration of neon?

1s² 2s² 2p⁶

What is the electron configuration of sodium?

1s² 2s² 2p⁶ 3s¹

What is the electron configuration of magnesium?

1s² 2s² 2p⁶ 3s²

What is the electron configuration of aluminum?

1s² 2s² 2p⁶ 3s² 3p¹

What is the electron configuration of silicon?

1s² 2s² 2p⁶ 3s² 3p²

What is the electron configuration of chlorine?

1s² 2s² 2p⁶ 3s² 3p⁵

What is the electron configuration of argon?

1s² 2s² 2p⁶ 3s² 3p⁶

What are valence electrons?

Valence electrons are the electrons in the outermost occupied principal energy level that are especially important for chemical behavior.

What are core electrons?

Core electrons are the inner electrons that are not generally involved directly in chemical bonding.

Why are valence electrons important?

They largely determine an element's chemical properties, bonding behavior, and common ion charges.

How can the periodic table help you determine an element's valence electrons?

For many main-group elements, the group position indicates the number of valence electrons.

What is the s block?

The s block contains elements whose highest-energy electrons occupy an s subshell.

What is the p block?

The p block contains elements whose highest-energy electrons occupy a p subshell.

What is the d block?

The d block contains the transition metals, where d subshells are being filled.

What is the f block?

The f block contains the lanthanides and actinides, where f subshells are being filled.

Why are elements in the same group often chemically similar?

They often have similar valence-electron configurations.

What are noble gases?

Noble gases are Group 18 elements with especially stable valence-electron configurations.

Why are noble gases relatively unreactive?

Their valence shells are generally filled, making them less likely to gain, lose, or share electrons.

What are metals generally like?

Metals are generally shiny, malleable, ductile, and good conductors of heat and electricity.