3 — atomic structure Flashcards
Atom
An atom is the smallest particle that can still have the chemical characteristics of an element.
Nucleon number
Nucleon number or relative atomic mass (A) = number of protons + number of neutrons in the nucleus (N)
Isotopes
Isotopes are atoms of the same element with the same number of protons and electrons but different number of neutrons.
Characteristics of isotopes
- Similar chemical properties because chemical reactions only involve the outermost electrons and not the protons and neutrons. (Same kind of chemical reactions can occur)
- Different physical properties because physical properties are affected by mass. (Eg density, melting or boiling point)
Groups and periods in the periodic table
- Elements in the same group have the same number of valence electrons. Hence they tend to exhibit similar chemical properties.
- Elements in the same period hav the same number of electron shells.
Ions
An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons.
Noble gases
Elements in group 0 have stable octet electronic configuration since their valence electron shell is fully filled with electrons thus they do not gain, lose or share electrons to form compounds. Hence, they are inert.
Why are atoms reactive?
Atoms form ions to achieve stable electronic configuration.
Explain why helium and argon are chemically similar
Both helium and argon are inert gases as they do not lose, gain or share electrons since both have stable octet electronic configurations with fully filled valence electron shell.
Suggest the trend in the melting points of elements oxygen, Sulfur and zinc. Explain. [3]
Lowest: oxygen < Sulfur < zinc (highest)
Both oxygen and Sulfur have a simple molecular structure in which small amount of energy is needed to overcome weak intermolecular forces of attraction. Hence they have a lower melting point as compared to zinc.
As Sulfur has a larger molecular size than oxygen, more energy is needed to overcome the stronger intermolecular forces of attraction. Thus, Sulfur has a higher melting point than oxygen. Zinc has a giant metallic structure where larger amount of energy is needed to overcome strong electrostatic forces of attraction betw positive ions and a “sea of delocalised mobile electrons”. Thus, zinc has the highest melting point.
Discuss the differences betw the way that bonds are formed in MgO and O2.
Mg loses 2 valence e- readily to oxygen to form Mg2+ and O2-. Electrostatic forces of attraction between oppositely charged ions result in the formation of an ionic bond in MgO.
Two oxygen atoms each share 2 of their valence electrons which results in the formation of a covalent bond in oxygen molecule.
Describe the similarities and differences betw the bonding and structures in diamond and graphite [4]
- Both diamond and graphite are made up of carbon atoms covalently bonded tgt.
- Both diamond and graphite have giant covalent structures.
Differences:
1. The carbon atoms in diamond are arranged in a tetrahedral structure held together by strong covalent bonds but the carbon atoms in graphite r arranged in layers of hexagons with weak intermolecular forces of attraction between graphite molecules.
2. In diamond, each carbon atom is bonded to four other carbon atoms but in graphite, each carbon atom is bonded to three other carbon atoms covalently, leaving a free electron in its valence electron shell.
Explain why graphite and carbon dioxide have different properties. [4]
- Graphite has a high melting and boiling point as there r strong covalent bond betw the carbon atoms in its giant covalent structure. A large amount of heat energy is needed to overcome the strong covalent bonds.
- CO2 has a lower melting and boiling point as it has a simple molecular structure made up of small carbon dioxide molecules held tgt by weak intermolecular forces of attraction. A small amt of heat energy is needed to overcome the weak intermolecular forces of attraction between the CO2 atoms.
- For graphite, each carbon atom has a mobile outer electron that is not involved in bonding, allowing graphite to conduct electricity.
- In CO2, all outer electrons of the carbon atoms r used in bonding w oxygen, thus there r no presence of mobile electrons or ions to conduct electricity.
Suggest why the radius of a lithium atom decreases when it forms a lithium ion.
A lithium ion loses its valence electron in order to form a lithium ion. When its valence electron is lost, the number of electron shells in lithium decreases from 2 to 1, thus distance between valence electron shell to positive nucleus decreases, atomic radius decreases.
Compare the bonding and structures of the poly(propene), silicon dioxide and propanol [4]
Structure:
All 3 compounds contain strong covalent bonds between atoms.
Propanol has a simple molecular structure while SiO2 and poly(propene) has giant covalent structures.
Weak intermolecular forces of attraction exists between the molecules of propanol and between chains of poly(propene) while only strong covalent bonds exist between atoms in SiO2 to form a tetrahedral structure where each Si atom is covalently bonded to 4 other O atoms.
